Having at least one summon will distract them to give you plenty of opportunities for backstabs.

Chain-gank the havel wannabe with your highest damage weapon before Andrei dies (Alfis is only useful to buy time), then counter gank the ganker 2v1 (do it where the archer can't hit you easily), then slowly torture the last one because that's the true reward for this god forsaken area

Weakness: standing behind a certain rock and killing them softly with ranged attacks

Literally pointless unless you want the flower skirt

How do I defeat them melee and offline?

Just flatten them with big bonk. Cast away your silly swords and magic, become bonke.

If Varg is truly a Havel Knight, and not just some imposter/random who's using Havel gear, I'm sure Havel would be very disappointed in him, No true Havel Knight worth his salt would team up with a band of graverobbers and gank you like a cowardly slimeball