The wellspring one is active, though. Yu can identify it by name when they use it. I mean, it’s passive in the sense that it doesn’t do anything by itself, but to get the mana boost they still need to activate it.
I don’t think this works. I think it’d just leave you unable to call on them (or, as you pointed out, any magic whatsoever), but I think they work off your bloodline, not your actual magic? There’s a lot of “I think” in that sentence though, so that’s a clear declaration that my actual stance is “hells if I know”.
Don’t phantasma die with bloodlines, not users? I mean, I’m not about to go prying into Sister’s sex life (just typing that is skeevy), but that’s a point to consider.