After i get jailed for killing the Iron Throne leaders, I'm sent to the catacombs. I kill a million dopplegangers then i meet Elminster and Gorion. They run ahead of me and I lose their trail. I follow in that direction then I meet Sarevok's gang. I can't beat them!!! It's not like I can retreat and explore and train, so what do I do?!?! A little help here...

Theres no other way out and thats a trap if you don't mind the spoiler they turn into dopplegangers just try blasting them with everything you've got and the dwarf is a friend so get his help if you haven't already told him to bugger off just keep saving and resting try not to take all of them on at once if you aren't strong enough to handle it, get one of your characters to go close enough to set one of them off and get it to follow you back to the rest of your party and then kill it.
You are just gonna have to battle your way through, keep your theif (if you have one) detecting traps cos yeah there are a few traps.

Hope this helps

What I mean is, I've already killed all of the dopplegangers... Then I meet up with these impossibly strong ppl who say they're Sarevok's gang. Ya, I know about the dopplegangers and that wasnt too hard to kill them, but i cant get past Sarevok's gang in the cave...

'cause they're impossible. You have to use all your wands.

As I recall I used spells wands and various magical items to summon wave after wave after wave after wave of monsters to fight on my behalf. As they turned yeller or hostile to my party I used spells, wands, magical items, and arrows of detonation to set off explosions on the enemy. These explosions also conveniently eliminating nearby cowards and traitors who were unable to attack me nor retreat because of the constantly supplied circle of fresh troops surrounding them.

Personally, I kept everybody huddled around the door back to the catacombs armed with range weapons, then used Imoen to scout (while hiding in shadows) and draw the chief guy (Prat, I think) into their range. You have to exit before he can use his electicity spell. Keep doing that till he's dead, then move to the next one.