Both rabbits should be neutered.
If not, not only will it be harder to bond them, but more things are likely to go wrong and they are also more likely to fall out at a later stage - and possibly never be able to be rebonded because of it. Not worth the risk in my opinion.
Male rabbits can usually be neutered as soon as their balls drop, so around 12 weeks, then you'll want to wait at least 6-8 weeks or more before bonding, so that hormones have a chance to die down.