I got to nearly endof Ch5, jewel is back in its socket and Leanna on the point of opening the door to start the skull sequence. She says to go in front for her safety, whilst she does magic to open the door.

From behind two ghouls come and attack. I fight them and beat them (stupid Leanna shouts "what are you doing?") and I 'fail' quest because 'Leanna hates you'

OK I think perhaps I must not fight the ghouls so Leanna does not hate me. but I died.

So I try to stand off to the side of Leanna and fight the ghouls, same thing, I beat the ghouls and 'fail' because Leanna hates me.

Heck, what am I supposed to do? Or is this how the game ends?

hm... i can only guess but did you hit here while fighting off the ghouls? even if you didn't mean to it is a quite bad idea (e.g. fireball)

(yes it really is; also in mp *grmml* stupid mages not able to control their magic)