I assume you realize this composition isn’t optimal but want to go with it regardless, which is totally fine. If you’d like suggestions on better comps for farming dungeons I’d gladly give some, but I would recommend at the very least you go with a different spec for your shaman since having a melee dps with casters makes multiboxing significantly more painful. You could just go ele on the shaman if you really want your priest to heal but having your priest go shadow and the shaman resto would work too.

As for handling combat it shouldn’t be too difficult if you do end up going triple caster. Your warlock and mages damage will primarily come from a single spell. (Frostbolt and shadowbolt) so they will be very easy to set up (warlock dots won’t be worth casting on most trash). If you have your shaman go ele instead of ehance you could also do most of your damage with lightning bolt. Your warriors rotation will be a bit less simple; you’ll have several abilities to use (sunder, heroic strike, shield slam, demo, etc.) so for all of the buttons you bind to those spells on your warrior you just put another copy of frostbolt/shadowbolt/lightning bolt. With this setup you can spam whatever keys you want on your warrior and your dps’s will keep casting their main dps spell.

There are are some different spells you’ll want to cast on your dps toons of course, like a curse from your warlock for tougher mobs. For spells like that, I’d recommend you have a completely different keybind from the main buttons you use on your tank, and also on your other dps toons put their main dps spell on that binding so they keep casting when you use those spells. You shouldn’t bother putting any tank abilities on those buttons unless you’re constantly rage capped for whatever reason.

oh and of course put aoe spells all on the same button, so blizzard+hellfire and maybe a cast sequence for magma totem and chain lightning.

Since you didn’t mention healing I’ll assume you know that you should be healing with mouseover macros with that system isboxer has that shows your healers party frames on all of your windows (I can’t remember the name of it atm lol).