My mother In law will not respect my wishes...what do I do??

Ok, so I am very strict about how I want to my son treated, what he's fed, no kissing his face, etc. Well my son is 4 months old 15 lbs and is strictly fed. No rice cereal no nothing. I personally feel that my son should not have solids until 6 months at least, and when he does start, I want to be the one who starts him. Enter the MIL. She does everything I tell her not to do and represents everything I detest. I told her not to give my son water, she does it anyway. I tell her not to take my son outside in 90 degree, she does it anyway. So anyway....she buys all these baby food items and gives them to my husband and tells me that she wants to start him on the foods now. Of course my husband says no. Our son is watched by my husband's grandmother while we are at work (His mother has a 6 year old son that she cant handle and I want my son to be safe!) His grandmother went away for a bit and while she was out my MIL tried to feed my son baby food. My brother in law stopped her.