a strat that has kinda worked out consistently with the knife for me:
focus on the first daughter's legs (the ejaculate damage is the same as the legs, so more worth it to disable legs first), then afterwards keep switching between cock/torso/healing (attacking the cock gives you one free turn to heal as she doesn't attack even after recovering), and you'll eventually manage to chip her health down to 0
afterwards just focus on the second daughter's torso and alternate between attacking and healing, it is a VERY narrow window of win (the mother and first daughter pouncing on you doesn't drop you to 0 HP, so if you hard focus the second daugher, you can survive with 1 HP) but it is absolutely doable