Why didn't Inko have Izuku's healing abilities disguised as a quirk? There's a superhero that controls blood and a character that looks like he crawled out of the Cthulhu Mythos. Izuku having healing powers through consumption of blood wouldn't be that strange of a quirk in comparison.
It wouldn't stop other vampires from finding out that Izuku's a vampire if a child with a vampiric seeming quirk is an actual vampire if Aizawa is any indication. While it was more painful, in the long run nobody found out about Izuku's origins.
Izuku is being deliberately groomed by Sumi on the command of his biological father so he would remain helpless and dependent as possible. And Inko is enabling them because she's also helpless to stop them since her reaction is to hide things from Sumi or flee.
