Long time lurker, first time poster

I have two stepkids, SD5, SS8. I have been in their life for the past 3 years and we all get along very well. SD5 doesn't recall me not being in her life and seems to gravitate towards spending time with me easily. SS8 and I grow closer and closer as our time as a blended family evolves. I have been very fortunate in how wonderfully easily my relationship with the two kids has been.

Not so lucky when it comes to BM - although some of the other stories on here make me feel as though I have gotten off incredibly easy.

Both DH and I are starting to notice some adverse developments in the kids based on things that go on at BM's house. Unfortunately she has 70% and DH has 30%.

All three of us (BM, DH and I) work full time. During the day SD5 finishes school at 11:30am and SS8 at 3:15pm. Fron this time onwards, until approximatly 4:30pm they are with BM's parents so there is an added influence.

The issues are as follows:

-BM and her mother both follow SD around the house, walking two feet behind her at all times. She is fed as she walks around (instead of sitting at the table), she is dressed, she is still wiped after all bathroom trips, she is still given bottles of milk at bedtime.
-Neither of the kids have a regular, consistent or age appropriate bedtime at BM's house. They are typically up until 10pm on a school night and SD5 often falls asleep on the couch and is carried to bed.
-There seems to be unequal treatment of the kids. SD5 whines and cries when she doesn't get her way and SS8 is encouraged to just give in to his sister for a "quiet life".
-The kids watch tv and play video games almost 100% of the time that they are at BM's house. I am not exaggerating. DH and I will drop the kids off there and he will call 10 minutes later when we get home and the TV is already on.
-SS8 is encouraged to act childish and wimpy. He got into a snowball fight with a friend from school and BM was horrified and concerned that he "doesn't know how to make friends".
-SS8 plays a competitive sport and BM agreed for him to participate, however she won't take him to practice's on her time. etc.

This is concerning to DH because of the following:
-SD5 is acting like a spoiled brat. She refused to eat at our house, demands treats constantly and tells everyone what to do. She will tell her Grandma to sit down if she doesn't like her standing close to her, tells me where to put my hand when I am sitting in the car, tells her brother not to make certain faces, etc. When we call her on it she has a complete meltdown. She starts bawling and telling everyone that she hates them. She seems to be miserable almost the bulk of the time that she is with us because we say no to her and she just starts pouting. These are reasonable no's (no, you can't play Wii right now - no, you can't have a treat right now - no, you have to at least try your dinner)
-SS8 can be very "young" at times. Once he is at our house for a day or so he is running in and out of the house with his friends, falling off his skateboard and not caring, etc. When he first gets to our house it is a different story. He doesn't seem to have much much of a sense of responsibility and commitment. He isn't really aware of his surroundings, time, etc. He is starting to have slipping grades and his teacher has commented that he "needs more responsibility and independence". BM's comment was "I find him very independent.

Anyone have advice of suggestions? Both DH and I are "do more" type of people, we work hard to succeed in life and are active, engaged people. BM spends all her time on the couch watching TV and seems to be breeding the kids to join her in this lazy attitude.