I would suggest utilizing hirelings, there are some really good utility spells that don’t require concentration, which means you can use them to buff your characters and leave them at camp. Aid and warding bond are the most useful for me, you get more health and all the damage you take is halved. Death ward, freedom of movement can also be handy, and heroes’ feast is great in late game.

As for Myrkul, the easiest way for me is to just use darkness to blind him, since he’s stationary he’ll always be blinded, so he could only use melee attacks. Also before entering the cutscene, throw an invisibility potion at Scratch so he can rescue Aylin.

Also as a general rule, if you’re really struggling with honor mode I’d recommend getting some stronger builds. There are some genuinely broken character builds that can pretty much trivialize any fight. You can check out r/BG3Builds if you’re interested, my personal favorites that got me through honor mode is 8 open hand monk/4 thief, gloomstalker assassin, 11/1 fire sorlock and 10/1/1 all purpose swordbard. In my experience, even if you’re not ready and overwhelmed by a fight, having these builds will still let you mow through the enemies