For the record
It is entirely possible to have Minthara and Wyll + Karlach.
You do not need to side with Minthara to recruit her, you just have to not kill her.
Wyll and Karlach are only lost if you actually attack the grove.
Just don't do the grove vs goblins quest at all, and all three of them will be in your party together. They don't even hate each other like Shadow and 'Zel.
Only Min and Hal are conflicting companion choices, though there was a sequence bug that allowed getting both. I think it was patched. Clearly unintended, seeing as they shared a tent.
The tiefling npcs still die though, just not to you. That's my gripe with it. As far as I'm concerned, if I kill enough goblins, the roads should be considered safe and the tieflings should be fine.