My parents are constantly undermining me with raising my child! How do I stop their controlling?

I am a 30 year old woman. I was young and naive when I was 18 and had a child. I was married when I was 22 and turned out that my then husband had way too many problems. After 4 years of marriage, I was divorced and since my child's father has been put in prison. I am now happily remarried and have another child that is only 1 now. The problem I have is that when I was 18 obviously I continued to live with my parents with my oldest child for the first 4 years of his life and my parents helped raise him as I was trying to go to college and work and his father wasn't much help throughout all of it. When I did move out at 22 my parents were always trying to tell us how to parent my son and raise him, but my ex husband just put up with it as most of the time he wasn't even around. We divorced almost 4 years ago and he's seen his son a little over that time. Things have gotten worse over the years though with my parents. My son was diagnosed ADHD at age 5 (he sees a psychiatrist on a monthly basis) and has a ton of issues with behaving due to lack of discipline. He's constantly in trouble at school, talks back, is just outright disrespectful to any adult including me and my parents! I've so much as had to admit him to a hospital for a week because he was so out of control and facing being expelled from school for his behavior. Now that I'm remarried and I've been with my new husband for 3 years, my parents both seem to undermine any decisions my husband and I make and are constantly scolding me for how I'm raising my oldest child. My husband tries so hard to discipline my oldest child (being the stepfather) and my son is just outright disrespectful to him. I still have my parents, who are nice enough to help babysit 2 or 3 days a week due to my husband and I's work schedules, but the minute my oldest goes to their house he starts crying to my mom about the discipline he receives from my husband. Not 5 minutes after my mother gets him, she's calling me telling me about how my husband is too mean to him and how my son hates my husband. My child is completely out of control and it seems as my parents just fuel the actions by yelling at me right in front of him the minute he tells them anything and 99% of the time it's a lie! But yet my mother believes my son over me and my husband! He's always lying about homework, arguing, and I cannot get a grip on him when my parents are always contradicting every step of discipline my husband and I chose. I am very thankful that my parents help with my children so we can both work, but when it's literally tearing our family apart because we are being told by my parents that basically every punishment we try to uphold my mother calls and tells my son he doesn’t have to do it! If I try standing up to her about it, the first thing she does is threaten to not help babysit the kids. It's as simple as if I don't comply, then I am stuck with no babysitter. I'm barely able to make ends meet with both my husband and I working full time. Luckily his schedule is a crew schedule so I'm off on weekends, he works, but he's off 2-3 days during week and I work so we don't need a babysitter 5 days a week. And I would rather have my parents take my children than anyone else, but I cannot afford a babysitter. I do not want to take my kids away from my parents but almost feel as if I have no choice. It's either forbid my oldest son from being over there, or continue taking the constant battering from my mother about how we're raising my son. I was raised exactly how I'm raising my son now. My son is even disrespectful to my parents. So much that outside people are appalled at how he talks to my parents and treats them. I've brought all of this to their attention and it's as if my mother doesn't care. Yet when I was young, she would not hesitate to smack, , punish me for acting as my son does to her. But when he does it, he gets nothing. If I try punishing him for it, she tells him he doesn’t have to listen to me. I've asked her time and time again to follow our wishes if he's grounded or being punished, but she does not. He has 100% run of the house at my mother's. I'm deathly afraid that my son is going to end up following his father's footsteps and end up in prison like his father is if I don't get a grip on him, but I can't when my mother won't let me. No matter how I talk to her or what I say, she doesn't care and throws this back on how he's a "special" child b/c of the ADHA and his father's situation. Even the doctor's I've spoken to at the hospital about his behavior agree that he lacks discipline and my parents are a large source of his behavior problems. Of course when I told my parents that, they got immediatly mad and threatened to not have anything to do with the kids or help with them at all. I don't know what to do anymore. I'm to the point that I've already mentioned signing my oldest over to my mom b/c I cannot raise him without her controlling every single action I take. We