C.,
They really can't FORCE you to do anything you don't want to do, unless they are holding you at gunpoint. I know you feel like they are forcing you, but really you are LETTING them do this. They may be using all kinds of tricks like manipulation, bribery, even blackmail, especially emotional guilt trips etc, to get you to do what they want you to do, but ultimately IT IS UP TO YOU to do what you feel is right for your self and your child.
We face the same problem with my father-in-law, who is extremely religious (I am spiritual but don't go to a church). He is trying to pressure us into sending our son to Sunday school. I have to tell him repeatedly that we aren't doing that. It is not his decision.
If your family begins to do things like taking your child to church or teaching him things you don't want them to teach him, then you NEED to stand up for yourself and your child. If what it takes is restricting the amount of time they spent with your child, then so be it.
I know it can seem like they have you over a barrel especially if you are dependent on them for financial support or childcare. If this is the case, one big step to take is to do what you must to become independent from them. You will feel like more of an adult then. They may or may not respect you more, but at least you will feel more free to do what you feel is right.
You are the adult, but you need to step up to the plate and stand up for yourself if you want to be treated like it. (And sometimes, other people just don't change. My father in law never lets up. We just limit our contact with him, and hold fast to our own values and ideals, and don't let him wear us down.) HUGS to you. Just keep trying to do what's best for you and your child. Other people don't have to like it.