Family members pushing me around about my son

I have an almost three month old baby and people in my family and my boyfriend’s family keep thinking they can push me and him around because were young and we’re first time parents! I’m 19 and he is 22. It’s really frustrating because they think because they’ve had a few kids or babysat lots of other peoples kids, that they can just tell us what to do. I read a loooot about parenting, babies, etc while I was pregnant and I continue to do so. I feel very comfortable when it comes to parenting, much so that it feels like I’ve been doing this my whole life.

My thing is, I just don’t know what to do anymore. They keep getting very mad at me because I don’t do what they think I should do with my son. An example is that he is very colicky and they tell me I need to feed him baby cereal which I have read shouldn’t be given to them until 6 months of age. They try to force me to allow my 3 year old niece hold my son. Two weeks ago while I was on my anniversary date with my bf they allowed my 3 year old niece to hold him without my permission! They actually even got mad at me and told me I was silly and ridiculous for not allowing her to hold him again! Also, I don’t feel comfortable with any smokers holding my son honestly but it has already happened. My boyfriends mom is a smoker and it bothers me whenever she holds him but I feel like I can’t just tell her she can’t hold him since she already has before... And the kissing, omg!! My whole family and his try to kiss my son all the time and I keep begging them to stop but they do it anyway and play it off like it was an accident each time. Call me crazy, but I’m so protective of my son. I just feel a bit bothered and upset that I can’t just do what I want with my own son..