Have you already spent all your experience? If not, you could run back to your haven and increase some stats before challenging Othelios again.
Which weapons, armors, items and scrolls are available? Couldn't you afford a new equipment for your characters?
Without knowing more of your condition I can't elaborate an appropriate strategy..
The hint i always give is to increase in the main character Strenght and Stamina and concetrate in a few disciplines till they're mastered.
I would suggest (translation from my language) "Feed" "Blood Heal" "Obfuscate (just the 1st subdiscipline)" "Protean" and "Thaumaturgy" (the most useful but, unfortunately, available late in the game)
Then I'd propose to "waste" a character to master "Auspex" "Common Disciplines" (among which "Revive", "Haven's Door") Social Attributes such as persuasion. The henchman will be of little use in battle but will grant you unlimited gold ergo unlimited equipment, etc..