If I run round the outskirts of the battle and use my bow I can prevail eventually but again Jesan and Merandil are dead. If I ignore this fight and go straight through the gate then the same mixture of daedra are attacking Ilend Vonius. If I go to his aid we both die, but if I stand off I can manage to survive by myself by doing lots and lots of running and shooting
You're doing fine
Let 'em die
The AI on companions is pretty bad, they can't keep themselves alive after a certain point
As a general rule for future reference tell them to wait whenever that option comes up unless you want to use them like tissue paper
Keep yourself alive, You can get all the enemies eventually
That is just the way it is when you take the standard guard against level 19 monsters and it's best to just get over it
I don't know if the diff slider is going to help, its changes the NPC's hitting power in respect to you but not to each other
Maybe you can RP some funeral rights after
Essential, in this case Salvian, chars don't die anyway
If you are really concerned about companions then you might want to work on some mage skills
If you have illusion and restoration you have a chance, albeit not enough of one to get by with out reloads, of keeping companions patched up, but I have found it impossible to do that and fight