[X] (Bandit Horde) Only the leader has a bow - the rest are coming in to strike at you in melee. With the river at your back to prevent flanking, you can win this, you're fairly confident. Give it a fight.
[X] (Bandit Horde) Summon the door, get Eira and Helen in, poof it, and teleport someplace (write-in where: back to town). You may take a few hits in the meanwhile, and you can be certain the bandits will move to a new location before long, but it's a clean escape and lets you potentially report their previous location to Arnstey Keep. (Yes, just getting away will be worth some XP.)
[X] (Bandit Horde) Write-in: Eira manifests Skate on Helen. Helen picks up Eira and runs. Senaz follows by air, Suggesting, as she does, that the bandits won't be able to keep up and might as well not bother chasing.