Backing down from a faculty position. Future career problems? I've gotten myself in a tricky situation.

Before finishing my PhD I applied to several positions, both faculty and postdoc. I received offers for a postdoc position at one of the top universities in my field and an tenure-track faculty position at a good university with a very good salary. Since I really wanted to do a postdoc, I asked to defer the faculty position for one year and it was accepted. They made it clear however that they could only "reserve" the position for 1 year, any further delay would cancel the appointment.

Few months into my postdoc, we found out my wife is expecting and the baby (our first) will arrive the month I'm suppose to move to the new uni. This means that during the final month we would need to search for house in another country, have the baby, arrange for the move, prepare for the new position, move the newborn baby to a new country, find new doctors, etc. I cannot move alone (and don't want to) since it will be too hard on my wife (we have no family in either countries).

My current lab offered to extend the postdoc for another year. However, I would need to back down from my agreement with the other uni. Will this kill my opportunities for a faculty position the years to come? Will it put me in the spot of explaining at every future application that I'm not a badly educated person?

P.S.: just for the record, I was/am really looking forward for the faculty position and I'm not happy that I'll have to do the whole interviewing procedure again...
I suggest contacting the department that hired you (the department chair and/or a few colleagues you trust) and explaining the problem. If it is a good university in a developed country, it is almost certain they would have all kinds of resources (both formal and informal) that you are not aware of to help new faculty members with issues related to their relocation, e.g., housing, health insurance and health care, moving arrangements, and other relevant things to ease your transition. They may also be able to rearrange your teaching to allow you not to teach the first semester, so effectively you could arrive on campus a few months after your initial appointment date. This could be done informally or as part of the institution's official policy for parental leave. My institution for example has quite generous policies for such things, so you may be pleasantly surprised at how flexible they can be.

Remember, your new department hired you, so they are probably just as eager to see you joining them as you are to be joining, and would be just as disappointed if you don't come. Will the move be stressful? Of course, any move is stressful, certainly between countries and with a family. But when you weigh the short-term difficulties against the very long term benefits from taking this dream position, I think it is a no-brainer (at least given the information you've provided in the question). Good luck!