Welcome to FT, and sorry to hear about your wife's complications. If your wife is the only one in the family with the relevant UK ancestry, then I agree that it is a risk to arrive without her.

I would either consult an immigration attorney as suggested, or inform your prospective employer of the issue. Since your wife was planning on joining you in December, I'm guessing that if all goes well with the pregnancy and subsequent birth, that schedule can still be kept, which is only pushing back your employment by a few months. Most employers who are accustomed to hiring from overseas are very used to these sorts of scenarios.

Good luck,

tb