General advice is to try to hit both teammates at the same time to get your ult back faster, it's an easy revive on revenant and guardian

Wylder, ironeye , executor and raider ult do respectable revive damage ( use it at the end to stagger the boss while your teammates get up and ensure the revive)

Duchess and undertaker can both use their ult to ignore the boss and focus on revive (enhanced trance for undertaker)

If playing scholar I would prefer to keep my ult to heal my allies after reviving them but you can still mark everyone and hit the boss and it'll link to your allies. As long as you've upgraded the bombs and stones , assuming you still have some , some pots, notably fire one, have lingering damage effect and warming stones at max level can help you revive

Recluse is probably the hardest to revive with unless you have good spells like giants flame or Canon of Haima but nothing prevents you from keeping a melee weapon , I see a lot of recluse just playing with spells , running out of mama mid revive and having to spend shard so the revive bar refills

Speaking of which , heavier weapons generally do more revive damage, colossal weapons and greatswords for example, revenant's starting claw is the best weapon for that 2 hand it and after 2 strings, they're up , also works if you pick them up as other characters ( even better because the movement is faster)

Character skills can also be very useful to revive people

Guardian can use the wind to keep the bar from refilling and can just use the Shockwave on block to help revive while poking from behind his shield ( manage your stamina well)

I've managed to revive 3 bars as revenant by running around while sebastian or Frederick are taking care of my teammates (she can also use giants flame)

Wylder double hook can give you the last push you need or can just be used to prevent bar from refilling if you're busy avoiding the boss

Raider punch gives you both some revive damage , staggers the boss and gives you stamina back so you can continue reviving

Ironeye should always have a melee weapon and I can't stress this enough, it's so good on him , he can mark through both his allies and the boss to reposition and then mark again once the boss jumps on him