the current Alpha handle Akira or the other Alpha handle Katsuya are just one of the so many trial they already did. the voluntarily are most likely because the thing they want to reach need "human" to actually do it. or they already try to have a mind controlled human but still failed.
as for...
if her mother are already gone and why she still need pay the debt. or is it because she "unable" to get away from them and just don't want to end up like her mother or something?