D.P.
I don't have stepkids, but I AM a stepkid. There are some things in your post that seem odd to me:
"Handling HIS kids" These kids are part of the package deal.
"...Useless to spend money on something that will not be used" Really? If your daughter was with your ex EOW, would you want him to buy her some clothes?
"I thought about putting all 3 girls in the same room and putting them on opposite weekends so "place to sleep" is not an issue and making them start bringing clothes to wear from their mom's house." Do you mean split up the sisters--or does YOUR daughter go EOW to her dad's too?
Why are you & hubby communicating with his ex about the activity schedule and why "can't" you get them to their activities?
No it's not right to take their room away from them. How would that feel?
I'm sorry, you don't buy them any clothes, you won't do their laundry, you thought about putting them on opposite weekends, you miss their activities...what exactly do you DO for these kids?
I'm sorry, but it sounds like the last thing you need right now is a baby.