I'm really thrown off by the mother being ~15,000 years old, that's about 3 times older than recorded human history. Then the big sis is ~290, MC and twin ~230ish, and little sis ~180. Even the cat and dog girls are over a hundred. It's all strange but when you add in that the twins and little sister are students I find it difficult to suspend my disbelief.
Like, what was mom doing for an entire fifteen thousand years before realizing "Huh, I've got about a quarter of my lifespan remaining. Should probably have kids.". What the hell are these "elfs" studying for it to be acceptable to remain students for centuries? The cat's bit of lore makes the age more believable, but how the fuck is this mutt doggirl so old?
Maybe it'll make more sense once there's more than a morning breakfast in the game and worldbuilding has a chance to shine. If it were me though I'd tone down millennia and centuries to centuries and decades.
Elf girls fuck cats.
It's a joke, so far there's nothing to imply the cat is MC's sister.