1) before having the fight with isbael
I meet raelag, after the CG, nothing happen.
He did not join my team, is it ok?

2) I won the combact with isbael but I am still not able to complete the mission, why?

If you have a savegame before meeting agrael make sure you don't have 7 heroes already.
There should be 2 heroes joining you.

I have exactly the same problem. I only have 3 heroes (Godric, Findan and Zehir). When I go through the first blue gate, I have the animation with Raelag & Shadya but they do not join my team. Then when I win the fight against Isabel, I have the animation of the Rituel, the objective is fullfilled, but the second objective (Findan, Godric and Zehir must survive) is never acheived, whatever I do... As a consequence the mission is never accomplished and I am stuck.

Very frustrating.

for me, i can't beat Isabel's ~500 Paladins..echm..yes..i'm sure that i saw about 500 of them . that erodes me psichologically..

I do have all 5 heroes. What I'm looking for is the best way to defeat Isabel, which heroe, what troops and how many and which spells are the most effective?

i used realag because his spell power was insane (2000 damage for meteor shower :O) but i think i ended up going in pretty much equal in monster count and didnt have too much of a problem. i went with the angels.

as for realag not joining. it sounds like its just one of those bugs and you'll probably have to restart the mission.