Consistency in early childhood....?

I will try my best to keep it brief........My step son is 3 and his whole life has been the center of a nasty custody battle......Bio Mom used cocaine and prescript meds and drank heavily in the first few months of his life, bio father is doing well.......the courts seem to keep siding with the bio mother because she promises the world (like agreeing to drug and alcohol test) and NEVER does any of it but the courts keep increasing her parenting time...she used to only have the son 8% and it has gone to 50% without her complying with one court order. When my step son is with her- she does not feed him properly, there is no structure (ie; bedtimes, discipline, parental guidence with TV or video games) he constantly comes home with scratches and bruises, he has started calling her "mama chocolate" and when he returns here he is cursing, throwing horrible tantrums, cries in the middle of the night about movies he watched like GI JOE and Aligators eating him. He wants to be at his Bio Mothers house (she is staying with her brother who is on his way to prison, she has no job and is borrowing a car from her ex bf) I understand why at 3 he wants to be there (its like disneyland to a kid) The courts are going to keep it 50/50 even though she cannot p a drug test.......Ultimately I am led to believe that my husband should give her custody...then when he goes to kindergarten the school can report his behaviors and we will have a better chance at the court listening....It is braking my stepsons heart to go back and forth (we trade 2/2/5/5) and he literally hates being here because we do not feed him chocolate for dinner and he cannot kick the dog or hit his brother....what is better for a child? A lack of consistency or 2-3 yrs of a bad environment? There is not one therapist that will take him on because its a court issue....I am running out of ideas! I truly want what is best for him and I know that our home is but the courts are "giving her a chance" as they say- even though they will not hold her accountable for much of anything....what is better for the childs mental growth? I know it would be best to not have to go through this at all but with the two choices what is one to do?