The girl in the gown is definitely either one we know or gonna be a new heroine.
That said, I also don't actually think his family is thaaat unreasonable, at least by crazy manga family standards. Sure it's only been a month, but look at how many times he could have died. The fact they even just let him choose to pick for himself in the first place is kind of surprising. Also, while sensei is creepy af, I kind of expect granny to be... Not 'nice' per se, but I think this'll end up being some ssort of test.