Sacred Haven of Debauchery

We could have handled it, even though Marcus sometimes "betrays" us.

If I'm not mistaken, he summons 4 Death Knights, in pairs, each turn. If your party is equipped similarly, you'll hardly be able to cope with them. But even if you defeat them, by that time, a whole horde of other summoned creatures will rush in. I personally solved this problem by killing Melchior as quickly as possible, but hardcore players consider this place extremely useful because you can gain a lot of experience by killing the creatures.

Added after 48 seconds

Is there anyone else here besides Arandor?

There is, but you specifically asked about Arandor, so I gave my opinion.