You just have to get them to a point where they're willing to date you. And TBF, the crone pretty much explicitly tells you "go for harem or die" at the beginning of the game, when she explains that you'll be facing a great evil, that failure will be disastrous, that you'll need all your faculties and to practice your mind control skills as much as possible, and that she doesn't care if you use it to sleep with girls as long as it helps you towards that greater goal.
glaurung, there's one more condition you're missing: