Snort at DH's earnest protests it's a once in a life time event! (When she's been married before) Just... Such a.... Man thing to say. 
My DC are too young for school but I really wouldn't want to pull them out for a 2 day extravaganza with a haughty bridezilla and brotherzilla, no less Even though the missing school would be my main concern, I think hauling 3 children that age to a hotel and a wedding = misery for you. I know you have to go, and I would (and have) too (thank GOD my brother and his partner are hippies against marriage) but I wouldn't be impressed. In fact I'd be all smiles and when finally home, quite exhausted and shitty at the family pressure and bridezilla wailing if you didn't bring DC. I know the feeling...
But I hate extravagant 'us,us, USSS!!!' weddings and I especially would hate being in the car with my three monsters DC for four hours each way. Like I said, I'd do it, but I wouldn't enjoy it and I'd probably end up in tears of exhaustion/rage because I'm highly strung whilst DH looked on blankly, not understanding.
I really sympathize OP, early education is extremely important to me too (especially since DSS has SN) and I'm fairy certain we're married to the same man... Sometimes I cheekily want to get him a 'Frankie says RELAX' shirt since he's so bloody calm all the time.
My post is useless but I truly empathise at the frustration of a relative bridezilla (my side, insisted DC be there for photos to make her look good, bitch) and a relaxed, up in the clouds DH who doesn't see your point. I say enjoy the bar and let your DHzilla drive home and take care of the kids. This is what Mean Mummy here did on a no choice wedding. TBF I was seething, this family member was: Hens night self paid + gift, bridal shower, organised as a 'surprise' and I was expected to contribute and hep organise + gift, bridal party (I don't know the difference either
) + gift as well as a cash present only -firmly stated in the rules, including an envelope with your name AND how much you gave on the front!- plus a bloody cash bar. Even DH was ashamed of my said family member when it all started to unravel. When I told him I was drinking and he was on kid patrol I didn't hear a peep. He's never mentioned it but I still remember the bloody year from hell. The worst part? I've left stuff out so I can't be identified!!!
This family member turned into someone I didn't know, she's actually quite normal. I still am thankful once her carry on began I turned down bridesmaid... Those poor women had it even worse than me!
Ahem.... Excuse my rant, just trying to say I identify with a doe eyed hubby he thought he'd get the bar... HAH! And a bridezilla. 
Good luck. Try to enjoy yourself and not kill the blushing bride or your DHzilla. Breathe, enjoy the bar and force him to drive and handle DC. Remember,it's a once in a lifetime event he wants. Make sure he's sober enough to remember every. Single. Detail. 