For your pally, you need to get some enchants: 45stam/15agi patch to legs, 22stam to boots, 20 Def to shield, 40stam to bracers(expesive but worth it), 16 def to Cloak, 4k more rep with AC for your helm enchant. I would also head to UP and do the Junk in my trunk quest for the Silver-Plated Battlechest. It also gives your priest a nice chestpiece, Bauble-Woven Gown. The whole quest can be done without killing one boss, you might need to reset the instance a few times. >.> I usually complete the quests on my characters before I hit the second boss. Maybe replace Glyph of Cleansing with Glyph of Divine Plea, it'll reduce damage by 3% while Divine Plea is up.

For your priest, try the first boss in H UP for Sorrowgrave's Breeches. The fight isn't that hard, bunch up your casters on the stage during the dialogue and tank her on the stage facing the seats. Kill the 3 adds when one of your characters get sacraficed, then reposition the character that got sacraficed. Get the Bauble-Woven Gown from the quest there too. Get Icewalker to boots, gem your pants with cheap int gems for now, sp or int for your belt. You can also get the frostsavage shoulders and bracers for your priest. Disc works on Int, crit then sp. Silent resolve isn't that useful anymore, Reflective shields gives no threat. I'd go with inspiration in the holy tree. Holy specialization is good, the other 5 points needed for Inspriration are a preference. Greater heal is hardly used, neither is renew. I'm not familiar with mages so I have no advice on them. Probably not what you were looking for, however I hope it helps.

For the Sladran fight, I actually tank him at the top of the ramp near the entrance with casters on the other side of the ramp. That gives me some time before the snakes get to me and the casters out of the poison nova range.