New here. I am in a relationship with a man who has a 4 yo son from a previous long-term relationship. We've been together 2 years and he has 50/50 custody with the BM, who I do not have a close relationship with. We are pleasant when we see each other but I do not interfere or insert myself in co-parenting between her and my bf.  

BM has very different parenting philosophies than we do. She thinks even the slightest discipline or correction to a child qualifies as abuse. To say she doesn't have boundaries with her child is an understatement. She coddles, drops everything to do the slightest task for him that he can easily accomplish himself, helicopters, etc. SS is afraid of everything, melts down to the tiniest correction, acts like his leg is cut off when he gets the tiniest bump...you get the picture. 

Lately, when SS is here, he is bratty, demanding, and uncooperative. He's a very intelligent child but due to the coddling at his other home he expects the smallest age-appropriate tasks to be done for him and it's a battle to raise him. Since I've been in the picture I've established a lot of boundaries in our home. SS is expected to sleep in his own bed (we sleep trained him at 3 yo--BM doesn't get him adequate sleep because she cosleeps and he goes to bed when she does/gets up when she does), help with picking up his own toys, take baths when asked, etc. Due to the stage he's at now, it's been a struggle to say the least. But it's also very apparent he gets away with refusing to cooperate whether he has to do things at BM's. She never tells him "no" I've personally seen her give in a dozen times to anything he wants within a 1 hour period. If he gets aggressive or screams in our faces, he is sent to a time out, otherwise for the most part we "gentle parent" or are authoritative parents. 

BM confronted us the other day during an exchange. She threatened court because SS says we "make him do things he doesn't want to do" and tells her he doesn't want to be with us on transition days (he does the same to us in regards to her when we drop him off--"I don't want to go to mama's/I want to stay with you forever/etc."). He also expresses these same sentiments when he is being disciplined or doesn't get his way in our home. Screams that he only wants/loves his mom, never wants to come back here, hates us, etc. 

How do we raise a child with respectful boundaries without court being threatened?! And how do we curb these behaviors? I'm at the point now where I am excited the day he leaves to go to BM's. I care about him a lot and do my best to be gentle and fair, but he's been a nightmare lately. I know that my bf losing parenting rights would break his heart and I will do anything to fight for his child, but I don't know how we can keep boundaries and keep this child appeased in order to stop the threats at the same time.