You need to give up the Sunday School. You didn't have 'a calling', the church and your in-laws 'called you'. God doesn't expect us to neglect ourselves, exhaust ourselves, or be bullied into doing things we don't want or feel able to do. At this point, you can best serve God by being a non-tired, non-miserable mother to your own child. Being a good parent is (IMO) God's highest calling. As far as FiL being the Bishop's boss, it would seem to me that the Bishop should have to answer to a much Higher Authority than your FiL!
It sounds as if you're in a somewhat patriarchal church or is that just your husband's family? Why should you have to be worried or concerned about how you speak to your husband about things that are bothering you or asking him for help? God teaches men to 'love their wives as Christ loves the Church'. Is your husband loving you that unselfishly when you are exhausted and all he can think of is for you to fall in with what he wants to do of a weekend? I don't think so. I was raised in a basically patriarchal church, the man is the head of the home and all that. But let me tell you, although my father considered himself the head, he never made a single decision without first considering how it would affect my mother and talking to her.
At any rate, there is no reason you should be doing it 'all'. You have an absolute right to expect that the father of your child will pitch in, especially at weekends. When I was on maternity leave (we have 2 now-grown children) I did it 'almost all' but my DH certainly pitched in on the weekends and in the evenings. And he got off work at 2am! Our agreement was that he could sleep in on work days but that Saturdays and Sundays from 2-4 pm was my sacrosanct nap time. He cared for the children and I went into the bedroom, closed the door, and slept.
Unfortunately, you've allowed things to get out of control and now the expectations are that you are 'Superwoman'. Your going to have to put your foot down and demand help from your husband and respect from your in-laws.
Who told you your child wasn't eligible for a UK passport? Was it your 'D'H or his family? Perhaps someone who may have had an 'ulterior motive'?