What do i do about a manipulative mom?

when i was a teenager, my mother was an alcoholic that cheated on my step father while he worked to pay the bills. there was a lot of abuse in our home, and in order to cover up her own mishaps and keep the spotlight off of herself, my mother made me out to be a terrible child. it caused a lot of emotional damage. now i am a 24 year old mother of 2. i had my oldest son who is 6 at 18. he was born early with a medical condition weighing 2lbs 9oz. when i first brought him home at 4lbs, i was terrified of him, and his father never really helped me. i realized i just wasn't ready for it and felt like a terrible mother. i was never a party girl, and i never did drugs (i don't smoke or drink to this day and could care less for it). i've been more to myself and stayed away from trouble. i've always been the type of girl in search of the family i never had and played a little house wife since i moved out at 15. bringing home a baby at 18 was overwhelming. so my parents being the only people i had for help, i decided the best thing to do was to ask my mother. she raised my son the first year of his life as i struggled to put our little family back together again. from the first day i asked her for help, it was if she acted like he belonged to her. i even found out she was going around telling people he was hers and never anything different. i just brushed it off as one of those new proud grandparent jokes. when he was 2, i realized what i had been missing and spent a lot more time with him. he did stay with my parents more often them myself as i ended a 5 year relationship with his father and moved into a new relationship with someone i wanted to make sure would love not only me but him as well. with my new relationship established, we started our own little family with my son. my mom still tried to act like she was in charge and sometimes i would give in to avoid the drama. i now also have a 2 year old, and we have a great little family, but my mom is still pushing it. last year my 6 year old started school, and so far my mother has knocked me out of going on every field trip with him, is pto mom, shows up at every little function they have (she sent my dad on "dad's lunch day" along with my son's step dad), shows up to pick him up for school the same time i am waiting in the parking lot for him, and she even took him to the dentist to have his 2 front teeth pulled out and didn't tell me until i picked him up at the end of her weekend. it is really starting to get to me, and i don't know what to do about it because my mom always threatens to have ssi and ebt benefits cut off if i even so much as not let her see him when she wants. she's offered me money for him and said i could even keep his ssi and all other benefits if only i would let her have him (that's just sick!). it's not about the money! it has never been about the money...at least not to me. after all, when she kept him his first year, she also lied to the state saying i lived with her as well drawing child support on me until i was 19 (she begged me to go to college so my dad would have to pay longer, but i caught on), ebt benefits on me, and i let her keep my son's ssi check because i knew he needed it for things that he needed. i have to admit it did freak me out when she was setting up a crib at her house while i was pregnant and setting one up of my own at my home (and i'm not talking just throwing together something for him to sleep in. she bought bumpers, curtains, wall art and all!). i'm at wits end and ready to pull my hair out. i've never had help with my now almost 2 year old. he's been with me since day one and never been baby sat for more than 2 hours. i now regret my decision of ever asking my mom for help and admitting i was too young. i appreciate her help, but i was hoping she would understand that with time i would come to my senses and grow up. i hate that she has to be in control of everything even after i have proven myself to be a fit parent, and i feel like she may be going through a midlife crisis and is clinging to my child. any advice for me?