Question about stepson's routine? Serious, experienced stepmoms only?

My husband and I get his son every other weekend. The boy is 5 and still sleeps in bed with mom. Also, she lets him stay up very late (sometimes 11 p.m.) while watching TV when he has pre-school the following afternoon. (halfday). When he comes to stay with us, I try to have him in bed by 9:30, and his daddy will read a book to him. He will not let his Dad leave the room after story time, he screams so violently and says he doesnt want to be left alone. (He has his own room at our house). I know we are changing his routine when he's with us, but I believe it's for the better. Am I doing the right thing? Any suggestions? Any other stepmom been through this? If you need any more info, let me know, and I'll add it. Also, he has a baby sister on the way, who he will share a room with until she is 2. I'm afraid he will mess up her routine.