how do i get my parents to back off?

I have a huge problem with my mother and step father. I live with them as well as my 3yr old daughter (and im also currently in my last trimester of pregnancy with number 2) my partner and i are building a house so i dont have much choice where to live at the moment. Lately no matter what I do they overwrite my parenting, I ask her not to do something or to do something and they will say "oh just let her go, she's alright" or "dont tell her off she's not doing anything" which I feel is teaching her not to do listen to me. My mother is very very controlling and tries to parent her and tells me how wrong im parenting all the time and passes it off as "advice". They both step in on everything with her!! Weither its making lunches for kinder, taking her out for the day (without asking mind you), punishing her, giving her phones and ipads after I've said no, sneaking her chocolate or lollies when I've said no, daily routine things that I should be doing, and even change overs with her father where Im meant to be present for. Im getting so sick of it but when ever i talk to them about it they just start fights or turn it around on them selves and start saying i have a difficuly child because i dont parent right, even when i say "im a young mum, im still learning" or "this is my child, im her parent" they completely disregard it and are back doing the same things within a couple of days. Now im expecting number 2 im worried and so stressed that they are going to take over again with this one and im going to start having more trouble than it's worth, my mums even started telling me what to do as my birth plan and who should be present in the room and even which school I send my next child to and how i should raise him because "he will have ADD" (my dad, partner and brother have ADD)... Please help, I feel like im going mentally insane to the point where I just want to go back in time 8 months and tell myself to wait on having more children.