Is it possible to sustain Infernal legion minions?

Infernal legion deals fire damage to your minions, so get their fire res to 90% (entirely possible to do using skill tree passives)

This means infernal legion will only take 2% of their life per second, so now you just need to get their life regen to surpass that which shouldn’t be too difficult between passives and gear

Yup it does not take too much work to get sustainable - even on a wasp which has a -30% fire res base penalty. Pretty much all you should need is on the tree: Crystalline Flesh, the small fire res nodes next to Regenerative Flesh, Living Death with the small fire res node next to it, then Vile Mending for regen. To sustain Infernal Legion III, it helps a lot to get a Heart of the Well jewel with minion regen.

It used to be with cast on minion death casting flame wall and infernal legion flaming skulls. They've nerfed that twice now to stop it.

You might be able to make it work with enough energy mods?

I have no idea if it's scalable in actual high-end play, but you can totally get skeletal brutes up 100% of the time with just death march and/or a couple skeletal healers. My very first character in POE2 was an infernalist using this with detonate dead and had no issues at all with uptime even before death march existed.

Of course this was back when meatshield scaled minion health by 50%. You might try the wolfpack with death march as well. I think there's a decent amount of companion health scaling though I'd have to check the tree and I'm at work ATM.