From what I recall reading, I have no clue or recollection of if the old granny becomes young enough to suit the MC's tastes and gets added to the harem. To anyone curious, it seems that the site that held the translation is no longer offline and requiring the wayback machine, so you can easily find it on Novelupdate, though there has been no updates since 2023.
But everything points to the idea that it is inevitable.
If we think rationally about how this is clearly aiming to eventually become a harem, you can probably figure out how Cost Sharing functions.