Celsie, you have proof he offered you the job - if he withdraws it because you're pregnant that's discrimination and you can sue his pants off. Do it. Your dad only has a few months more there, if they sack him because of you then he can sue too and make more from that than he would in the few months.

Sign and accept the contract if that is what you want; once it's been agreed then it's even harder to take back. Good luck with it!