I'm not as into moms... Aunt's are ok, but meh.
Dreams of Desire, Big Brother, and Sister Sister Sister.
Parental love has some planned, but said aunt is the in-law, not sure if that services your fetish.
I also know View of Family has some planned, but I'm not sure what's going on with that, is it on hold, is it abandoned, who knows.
I think Kinney was Avoiding incest, despite his game being almost all about it. But you could see if Beth and her little sis ever do anything, I'm not sure if they do or not, since I haven't played the recent versions. Inevitable Relations.
If ICCreations ever does continue IC in Paradise, which I think they aren't doing, it will have some for sure. And you could watch their current project F.I.L.F. to see if they do it there, ICcreations always has a mom and an aunt, though they never put the two together in The Artifact or Incest Adventure. (Which, if you haven't, you should play both before IC in Paradise, otherwise you won't understand it.)
While they aren't Milfs, and have no children, Blooming Love is all about Sister's who decide to start a lesbian relationship.