Moving in w my bf and his family

So I’m pregnant 18 weeks and we both agreed to move into his place with his family (his sis, mom and brother )because we figured it’d be better for the baby, I gave 800 last month to help them, when I moved in because they plan on building a studio in the back for me and the baby, my question is I know for a fact that no where will anybody live for free but if they claim me as family shouldn’t I live here for free till the studio is build? They want me paying 400 a month which honestly is better then 850 from my previous studio I guess it’s really not the money for me it’s more like my bf not helping out or paying shit cus it’s his family and yet me being pregnant I am paying rent. Maybe I should just let it go and think of it like nothing in life is for free or am I wrong for feeling this way