Where does SD24 live that she needs to come use your home? I read your update that said you have three skids ages 22-26 yrs old. 

These are full grown adults. You mentioned SS22 still lives with you and his father. Why? It appears from her insistence of bringing her slept-over BF to your home and using it in your absence that SD24 might be living with BM? 

So what's the plan with these adult skids? Are they all still in college or just like mooching off of Mommy and Daddy? 

If they need a 'room' with a BF, I assume the BF doesn't have a house/apartment of his own either? 

Whip that 'welcome' mat off your front step. There is no reason for these adult children to be anywhere near your home when no one is home. They shouldn't be over at your home unless invited or having called and asked if now was a good time to swing by for a visit (a short visit, Sunday dinner, family birthday party, backyard BBQ, pre-agreed 'need to talk to Dad'. Blah blah).

Dad needs to work on getting the SS22 out from living in your home also. If nothing else, it's high time and besides, as long as he is living there the other two will use it as an excuse to come over and/or come when DH and you are not present. 

I'm going to ask if this happens to be the home Dh had while the kids were growing up or perhaps the one he had before you and he got together? If so, put it up on the market. Time for the house to go. You need a home where you are on equal footing and the house it truly 'our house' . Homes from the past are not good. Somehow kids, even adult children end up with the impression it's Dad's house and you don't count because you are the new comer. Buy a nice house together. One fairly small but comfortable with strict usage of extra rooms (such as the spare bedroom isn't a spare bedroom it's your home office or your hobby room or whatever). No room for adult children to move in and/or come crash. 

As to your DH's    "Now he says when is the shit going to end..."  , it ends when he gets the guts to lower the boom and makes it end. Does he want a home with a happy wife and life with her or does he want a houseful of grown adults running in and out when the whim strikes them that mooch and use the house as their hotel? You're not saying them or me, only requesting he set boundaries and stick to it. 

Think I'd start an Air BnB and let the kids know their rooms are rented out so they're not welcome now. Or hire out some ongoing messy remodeling projects with a very slow contractor so the kids won't be so comfortable with all the noise and paint fumes.  Bottom line is the home is you and DH's not skids. If they grew up there I can see how this may be an issue with them still thinking it's THEIR house.  That has gotta stop. This may be a hill to die on in your relationship, I had a similar issue w/the oldest ss just wanting to hang out since he was *homeless* and unemployed. It almost ended our marriage but the behavior ended and the locks were also changed.  

Ok, I know  most did not agree with me about adult skids spending the night (which I just don't understand) but why in the world does a 24 year old, who I'm assuming has her own place and who I'm assuming lives fairly close if she just pops in from time to time, need to hang out at your house all day when nobody is there???? 

Am I the only one who thinks this is strange as well???

I have a similar issue with SS21 wanting to freeload at mine and DH's house ALL the time. SS21 lives with his grandparents because he destroyed in the inside of the mobile home that DH gave him and it is now unlivable. Not my problem. He needs to get off his ass and get a job and find his own place to live. He will come to mine and DH's house and just freeload for days at a time because he doesn't want to be a his grandparents house. DH doesn't have the balls to tell him to leave and it has caused some marital problems. All of this to say, when you figure out how to approach this situation successfully please let me know.