Well, those two also followed the ideology of "the more sisters the merrier", so it didn't surprise Aster, also the blond roc mother had taken both red haired sisters as well as Dahlia under her "wings" literally and figuratively earlier, so it wasn't surprising that Sarina invited them to join them.
Though Lauren and Mira were indeed a surprise, but the same principle stands, Sarina is quite the motherly girl, so she also brought the badger girl under her wing, which is also understandable given how her relationship with Cassandra was more like that of a daughter and a mother rather than close friends which usually becomes like that of close sisters.
