So basically, it's a Tsuyu and Izuku sibling AU. They are the eldest of 12. They are twins, with most of their siblings being twins or triplets, this is because of their mothers quirk. All of them have either their mothers or fathers quirks or a combination of both. Izuku was born with a quirk, but because of how strong it is, doesn't use it, for fear of hurting others, so pretended to be quirkless, he still does get One For All though The only ones who know about his quirk is his family.
Tsuyu and Izuku haven't told anyone about their siblings, let alone them being related, because they don't want their family to get hurt. Not even the teachers know about their relationship, as at the UA entrance exam, they lied because Tsuyu put her last name as Asui, not Midoriya, which is what it is.
The reason for this, is when Izuku and Tsuyu were 5, their parents started drinking and beating their kids, who were protecting their three younger siblings who were only a year old at that time, and as they got older, it got worse, Inko and Hisahi, their parents started coming home later, drinking more, and hitting their kids more and more. Izuku and Tsuyu would always protect their younger siblings so they wouldn't get hit. When the youngest two were born, their parents just left without warning so Tsuyu and Izuku had to look after all their siblings on their own.
Most of the younger ones call them Mama/Papa, because they are the only parents they have known and all of them look similar to them and have simailar quirks.
All the younger siblings go to the same school, and the elder of them try to help out Izuku and Tsuyu, but they refuse the help because they want their younger siblings to enjoy their lives.
Both Tsuyu and Izuku work several jobs each just to keep their family fed, with clothes, educated and a roof over their heads.
Neither Tsuyu or Izuku get much sleep or eat much as they are either too busy and forget, or are trying to make sure there is enough food for their siblings, as they are paying rent and barley making ends meet, even with working several jobs each, but still go about their days like nothing is wrong.
I'm changing Inkos quirk in this, so it fits better with the story. Sorry if this chapter was long, the next one will be as well, because it is the introductions.