My sister had this issue and she tried 2 approaches

1. you explain to them before bedtime that they need to sleep in their own bed. You put them in bed, read them a story and say goodnight and leave the room. If they come out of the room you take them back and put them in their bed with NO communication. No words whatsoever. You do this all night long if you have to and it might take a couple of days.

2. The above combined with an award system. My sister made a chart with the days of the week and every night that they slept in their own room they got a star. Once they hit 5 stars they were rewarded with something small like stay up 15 minutes late, extra TV time, a treat from the store...this may not work for the 2 year old, but will for the 4 year old. Praise Praise Praise. Kids that age absolutely love it when you acknowledge or praise things they have done. Maybe the reward for the 4 year old could be a party! The first night that he/she sleeps in the room alone, have a party for them! Not a big one. Just the kids and you guys. Get some balloons and streamers and make it a really big deal how grown up they are and how proud of them you are, maybe have cupcakes or something on hand to celebrate this important even in their life.
Seems super cheesy I know but you would be surprised at what a 4 year old will do for you to be proud of them.

We changed the door handle so that the lock is on the outside. You must put the key/flat screwdriver in the room, in case you ever get locked in. I have done this for both my boys. My biggest concern was that they would get out and we wouldn't know. My oldest, 6.5, has had his door open for 3 years. My current 3 year old, likes to get up several times a night and walk around. I have started to lock the door on him. Now he wiggles the door handle and then plays in his room several times a night, it is a safe place, not like the rest of my house, who knows what he could get into. This lasts a few days and then he goes back to sleeping through the night.
You have to ignore them when they are crying, it only re-enforces that you will come in. It is extremely hard to listen to them crying in the other room, but they will get over it. When I ask my 6.5 year old, he doesn't remember me letting him cry himself to sleep. And boy he could go on for hours.

Slap em silly and send them to bed.

OKOK just kidding. I like the first reply. I don't like Daddy sleeping with them and I'm worried about fire in the third answer. In a fire 1/2 a second can make the difference between dead and alive. Ask any fireman.

Get USED to being the BAD GUY! ECHO is right on! HE must take the "little darlings" to bed and make them stay there. This is just a foreshadowing of your future. It will get worse before it gets better and most likely unless dad changes, it won't get better. One night my then 11-SD ran around the house screaming at 11pm not wanting to go to bed while my 2 ds were already trying to sleep. HE chased her around the table and was like a little deer in the headlights about what to do! He eventually put her to bed and my boys said she was "crying like a baby in a crib." BF ran back upstairs to make sure his little darling was ok. I kept telling him, "Please, let her cry it out" at which point he screamed in my face, "YOU ARE CRUEL! I CANNOT BELIEVE YOU!" Well, excuse me, a-hole, but I CANNOT believe a 40+ yr old man with a sociopathic ex who p.a.s. your son already is so clueless! Good cop/bad copy; letting you do his dirty work, whatever you want to call it. Stand tough now. If he loves you, you will last. If he is wishes to let his girl run YOUR lives, then start planning your new future. I stuck it out, but secretly sought therapy, counseling, cried in the closet and almost lost myself. Very bullied by sd and it was ALLOWED or else while my 2 ds and 1 dd sat in the wings. Not until I was ready to kick him out (and I'm not kidding), did he take me seriously and start instilling some discipline methods. How many times can a man let their teenager tell his SO (me) to F off? Charts, rewards, yadayada all very well intentioned, but believe you me, if BF does not take a stand, and be willing to be "punished" for it by his little darlings, then it is hopeless in my experience. I told my SO that even though his ex is so f'd up and evil in the head, he helped create these monsters by overcompensating for her neglect and emotional abuse. New here and relating to so much! Love the term "neglected puppies" that is exactly what his kids are at their BM's house, so they take it out on our family. As long as they think they have Dad's unconditional love (which they did until ss "left" and we then went in front of a judge to not let him back), they will always try to win their BM's love. My SO's son would be rewarded with prizes for causing a stink in our home. No. I am not kidding. P/s, I don't think it is legal to lock a kid in their room, and that is something i would NOT do nor recommend, though I do not judge when all seems hopeless. If your DH has an evil ex, then you are setting yourselves up for claims of "abuse" (or even by the girls themselves when they get older and decide they need to get back at you for something, say like not taking them to the mall) by letting them sleep with you if you get my drift. Now my sd is 17…fun times, not.
*Not my monkeys
Not my circus."

We had this issue. I use to think it was so crazy to have your child sleep with you in the the bed every single night until my husband deployed. He was gone about 6 months and when my children wanted to sleep in the bed with me I would let them. Of course when he came home we realized that I had created a monster. haha. We have finally broken my step daughter of it and now my daughter does it because of deployment. My point: you have to understand that the BM isn't letting her sleep with her to get under your skin. When you are use to laying beside someone at night and then suddenly you're not it is nice to have a body there. It is a complement for your children to want to feel safe beside you in bed HOWEVER it does interfere with the whole mommy daddy relationship/cuddle time.
The solution we found was simple: BUNK BEDS! or a large air mattress in the living room haha. If they don't want to sleep alone we say "fine sleep together!" It is only for a short phase. I promise when they get older they will out grow this part of it but I just wanted you to know that I understand the nightmare of bedtime.

PS leave your door cracked once the coast is clear for children to enter. If the weather is bad outside or they have a bad dream or a monster is under their bed they need to know that you are there for them.

Keep dragging them back to their own bed until they pass out from exhaustion. End of problem. The next night ... lather, rinse, repeat.

You have to be more tenacious than they are.

IMHO of course.

Read a book lie down with them shut the door and leave. Let them cry it out. Maybe a nightlight.

This is one of the smaller battles in step parenting or parenting in general and if you can't handle this one you are in for a horrible ride. The advice above is great. Keep bringing them back to their beds. Y'all giving into their crying is making y'all just as guilty for them being co-dependent. They are children, they don't need to be in bed with adults and I would think keeping them in your bed is not going to keep you and SOs relationship healthy either.

I still co parent due to past issues its turned into a security blanket at night for my boys and I. They are five and nine yrs old. If Im not in the bed I promise you noone is sleeping. Some nights they sleep together or they migrate or I migrate. My boys have had a alot of past hurts from a ex so its understandable the counselour says. Also for me I sleep better with them next me. One time when my youngest had croup he woke up gasping. I felt him twitch got his hreathing mask on and called er. Had he not been next to me it would have been different. We share a room at my moms about the size of a small bathroom. I never belived in letting my boys cry it out. I rocked and sang to them till they fell asleep and still do. Countless nights spent sleeping in the rocking chair. Funny part is my boys are social butterflies and do great with other kids and people. Im no help sorry.

It will be tough teaching them to sleep in their own bed if mum teaches them otherwise.

I'm guilty of having my baby in our bed about 3 nights a week. I find it very difficult to let her cry it out like my partner would want me to.

I can see how BM has fallen into that bad habit. I can see myself doing that if it was just me and my daughter and yet I know its a very bad habit to teach them.

You'll have to show tough love.

Do up their bedroom to what you think they like. if they like princesses do a pirincess theme for example. Get stickers for the walls and ask them to help you decorate the room. I don't recommend bunk beds for their age. But maybe, just maybe if their room was a fairy tale world they could escape to and look forward to perhaps they would enjoy their own room.

Also depends on your budget and space in your house - i.e. can you dedicate one room to be totally girly or does it double as a guest room?

Good luck!