I finished Planescape Torment on normal with no problem. i even defeated the last boss in my first ~ 4 tries. But both Baldur's Gate games are so difficult. With the Sarevok fight, i lowered the difficulty to easy, and even then i only killed him because of his crap AI which caused him to lose HP out of his own ally's cloudkill. Now i am playing BG2 and it's so difficult. I am doing side quests to level up for the main quest. My party is level 9. I am doing the Raelis quest and i have no idea how to defeat the bounty hunters in the portal without losing at least 2 characters
Are you talking about the battle right when you go through the portal? If so, have Jaheira drop an insect plague first thing.
As I recall there was an invisible assassin type who can one-hit a character. Be lucky with his first hit, was my approach, I think. I don't believe there's time to do any anti-invisible strategy before he does his thing.
If you are talking about any of the other battles in that setting, then they are all set-piece fights where you initiate battle yourself. You can do all kinds of long range stuff. Creative use of fireballs, earthquakes, poison clouds, etc. Or you can go with a torrent of summons.
Also some of the bosses can be lured so you face them one at a time. It's been a while since I played this so my memory may be faulty. I'm sure you can find video walkthroughs of these fights on the 'tube.