1. Is Inquisitorial Magic allowed or forbidden? The Book of Magic says it's allowed, but it uses the red icon like the forbidden books.

2. How do I use the Priest's "Mana Restoration" skill (or any other active skill for that matter)? There's no icon to drag into a quickslot.

3. Is there a way to heal your companions other than casting Healing Touch on them? Right now I'm at the start with only Diabolus, and he seems to heal himself somehow.

Diablus might be drinking your potions. As to skills, check your spellbook page and click on the button to the far right that is different looking from the spell schools, that will show both passive and active skills, along with icons. With mana restoration, I think you have to right-click on your character. This can be tricky. Most beneficial spells can be like that.

Thanks Sabin,

seems I looked in the wrong place for that skill icon. And yes Diabolus has been drinking potions I see now

You've probably figured all this out already but Inquisitional magic is allowed

If you open your spellbook up there is a skills section that you can drag the mana skill to your hotbar and use it there

By default followers can use potions so whenever they need one they'll use it unless you toggle it off