Ooh, wonder if nailak IS actually the OPs BIL, only a complete idiot would think the OP is BU... 
I wouldn't want to travel 2 flights, a coach with practically an entire day waiting at an airport even without DC, let alone a toddler and PG...
OP, you can actually fly up to around 30-odd weeks, give or take a week or so with some airlines.
IF DH wants to go, then he should go. IF not, then he genuinely doesn't have to.
Even if your BIL was actually paying for and fully compensating your family for the trip, if you don't want to go, he can't make you.
BIL's surname isn't Mussolini by any chance, is it? He has no right to dictate to anyone what to do with or without his money.
If I were you, I'd be telling BIL to take some of that £60k he has, and place a large bet on him still being married in 2 years time. 
Actually, that's the other point, there is a formula that needs developing. Working out the relation between the amount of sheer bridezillaness or indeed groomzillaness and the longevity, or lack of, of the actual marriage. The worse the wedding for this, the shorter lived the union...
This pair will be screaming at each other and instructing lawyers before you have even finished bringing yourselves back up to date with the debt of this trip.