De'Arnise Keep Options

[Olbas]

I am stuck in the Keep and was hoping someone could help me. I went down the keep stairs to confront Torgal but was unable to beat him(didn't try much though because still stuck on Greater Yuan-ti) and now I can't go back up the stairs. I can't find anything in the Documents about this so was wondering if it was a bug or possibly it happened in the vanilla game but I don't recall it happening.
Also I can't beat the Greater Yuan-ti and if I kill Torgal first then will he disappear and I won't be able to forge the flail?

Please can you advise me how to beat the Yuan-ti,

Party:

Kensai-11 Dual wielding Long Swords

Berserker-11 Bastard Sword and Shield

Cleric/Ranger-9 Dual wielding Flail and Hammer

Cleric-10 Mace and Sheild (Is a swash dual but too much experience away from getting those skills back)

Jan-10 mage/11 Thief

Edwin-11

Normally I have my fighters kill the spider and Jan and Edwin cast Breach, Remove Magic and Spell Thrust on the Yuan-ti and then send my fighters in to attack him. I continue Breaching to remove any stoneskins he casts however I can do hardly any damage too him before I am killed, the one time I got him to badly injured he cast protection from magical weapons and I lost. I'm not sure how I can beat him, I have tried slightly different tactics but this is the best I have so far.

[Olbas]

Thank you for the advice, it worked perfectly. I didn't cast Breach when he cast Protection from Magical Weapons because Jan was dead and Edwin was was lying down. Admittedly though I didn't even know Breach removed this protection and just found it it removes Absolute Immunity aswell! I've never had to think about what removal spells to cast before in any other Tactics mod, well done on a great mod and It will definetly make me a much better player.