I can't say with 100% certainty what should or shouldn't happen, but I'm pretty sure Malady helping you is not a given. It seems to require a bunch of conversations with her along the way (and maybe some other stuff).
The same for Jahan going to fight the Doctor by himself. There's a lot of things involved in Lohse's quest, which is why it's hard to tell why something happens or why it does not, without digging deep into the codes. Helping Jahan with the business on Bloodmoon Island, learning the demon's name, among other things. Again, I might be wrong on this.
As far as fighting the Doctor goes, it's possible to do it in the worst case: having Lohse in party, fighting him when he's at full power, in demon form, in his office, on Tactician, etc. This is hard to pull off, naturally; you need a strong team and specific tactics. Otherwise, you can always try to flee. Granted, this is one of those situations in which it might become very difficult to back out of unless you have a good previous savegame. If you start off the fight in front of his room as normal, you will be surrounded by enemies and even fleeing would be a problem, unless you have Escapist, used in combination with the teleporter pyramids. What I would suggest in this case is, try to back up toward the door while killing off as many minions as possible so that you can run away.
I don't know what exactly you have gone through during this quest, I'm just saying that it's possible that Malady and Jahan not showing up is not a bug in your case. But if you have been thorough all the way and develop their involvement properly, then it would be a bug.
Last edited by Try2Handing; 30/12/17 03:24 PM.