I’m not 100% sure if this is a bug or not, but my achievement popped from a vial Aphra threw.
If companion attacks count towards the grind, these achievements are just a matter of playtime with certain companions. If not, definitely invest in the instant trap placement upgrade (only needs 1 point) and spam the elemental traps when surrounded. Most of the beasties are resistant to everything except for that so it does a decent amount of damage.
Poison traps are also great as they double down towards the poison achievement grind, though upgrading the bomb ultimate will knock that one out in no time.
Also, vials may count towards this (since Aphra’s apparently counted for me) but I never messed with them so I’m not fully certain.