First, congratulations on your decision, I hope everything goes smoothly for you.
If you are concerned about this now, before you are even pregnant, and these domineering people have that much influence over your life and happiness I would also suggest waiting a few months. Pregnancy should be a wonderful time and if these people can do that much damage then I'd side step the trouble.
Mind I'm not saying what I would do myself because it's not about me. If these are your circumstances then it's best to work with them, not buck them.
As an aside, some people, like me, get pregnant the first time the first month off BC pills. When it happened i was stunned because everyone I knew had such troubles, I thought it would take months or years. Anyway... lesson learned was don't assume other people's experiences will have anything to do with you. Don't start unless you want the baby 7-10 months from now.
Good luck