Idk what to do

I have two step babies and one is 4 he will start elementary school next year. I have been fighting to get him in preschool, speech therapy and well anything to help him. He has made huge strides in the last 6 months but he is really behind. I don’t know what to do and how to get bio mom to do what I say. I know I’m sounding a bit harsh but I am the one that potty trained him, I’m the one getting him to eat new and different foods, I am the one that has been teaching him everything. For example he misses his mom when he’s here. I ask him what she does and I bait him to say nice things like does she cuddle you, play with you, read to you, watch tv with you. No, what Mom does is open the door to grandmas house and gives him the remote. Mom lives on the same property as her parents. I’m livid! He deserves better!!