Tips on dps setup for my team

[Wubsie]

While simply binding similar spells to the same keys can work to an extent, it's going to be very inefficient in the end. For mixed teams you'll usually want some way of creating "rotations" for your characters to go through. Most commonly people use either an addon called Gnomesequencer (I'm fairly certain there will be a classic version) or the ISBoxer pro configuration. Some people also combine parts of both, which is fine as well. All very much dependant on how you choose to run your team.

[Apatheist]

In your chosen setup it would make more sense in terms of buffs and efficiency to play the shaman as restoration and the priest as shadow. At least this way the shadow priest will buff your warlocks DPS and all of your characters will be ranged. I find playing one melee class (aside from the tank) with an all ranged team is kind of annoying.

Also, casters don't really have a "rotation" in classic. Warlocks spam shadow bolt, mages spam frostbolt. At lower levels you don't even do that if you have access to a decent wand it will do more DPS than your spells.