Same carrier is a little iffy if they're not fully past the fighting stage and you don't have a second person so that someone who isn't driving can break things up ASAP... however, most rabbits seem to be a bit catatonic during car rides - Nala and Gaz have always just huddled up and waited for it to be over
. If you'll be the only one in the car, I recommend a "dry run" tonight (or pre-vet trip tomorrow, whichever) where you're just driving around your neighborhood or something (ie where you can pull over at a moment's notice on the off chance they start fighting) - better to find out that they're inclined to fight in the car when you're creeping around a neighborhood at 20 mph than when you're on the highway or something!
Assuming the dry run is uneventful, then I think it could help to take them to the vet in the same carrier (with a second on hand just in case, if possible... if you don't have a second, you could ghetto-rig one out of six NIC cubes and some cardboard (for the floor) with a carabiner or something to hold it closed (failing that, a couple extra zip-ties... just don't forget to have scissors on hand to snip it open if need be + a couple more to re-close it
). I prefer the top panel to be the "door" but a side could work as well. If they *do* fight on the dry run, you could still take them both - just in separate carriers. I would definitely take both if at all possible since "weird vet office smell" can cause problems with a fully bonded pair so I would think it could do the same for bunns in the bonding process.
As for the "grooming wars"... I'd call it a neutral sign. It's a pretty common bonding issue and stand-offs over grooming are way better than actual fighting! It's just a thought with nothing in particular to back it up, but maybe you could try showing them the way, lol - get down on their level and "groom" each of them (rub your nose against 'em or something, you don't actually have to *lick* them
). Failing that, just wait it out - presumably someone will groom the other eventually.