I'd bet my limb on the mom and aunt being a sister couple.
Seems like the safest bet. Could be aunt and one of the mom's daughters, possibly. Less chances of that, but it's possible.
Chapter 1: First GuestsWaah, nice!The scenery is nice too! We chose the right place.It really has an antique Japanese inn's feel to it.Yeah.We were expecting you.Heh!Oh my.Welcome!I'm Tsukuda, I have a reservation.Hello.Please help yourself.I will take your luggage.This is my sister, Hana.Wow!They have a cute helper here!So this is a family business?Yes.Me, my mother, my aunt and two of my sisters all manage this place.And my name is Yoh.