I'm going to show some information about Quirks for those who don't know.
First; Quirks come three main types, and one sub-type:
Emitter-Types: These Quirks are activation-based Quirks that don't change the user's appearance. These powers are stuff like; Elemental Manipulation, Teleportation, or Psychic.
Transformation-Types: Quirks that change the user's body properties temporarily. These powers include; Size Alteration, making the user's skin as hard as stone or metal, or just Shapeshifting.
Mutant-Types: These are Quirks that feature permanent alterations on a user's body. Mostly stuff like, extra limbs, or animal traits. These features are hereditary, even if the child has a different Quirk, for example; the child of a user with a Mutant-type Quirk that makes them look like Godzilla, will also look like Godzilla, but their Quirk might be something else, like Teleportation.
Accumulation-type Quirks are powers that, in order to function properly, require the user to accumulate something ahead of time, such as power, energy, mass, or a particular resource. This is a Sub-Type.
Secondly; Quirks are hereditary, a child will either inherit the father's Quirk, the mother's Quirk, or a completely new Quirk formed by a fusion of the two. Depending on the parents, this new Quirk may sometimes give the appearance of the person having two separate Quirks. Naturally, since Quirks are inherited genetically, siblings tend to have the same or very similar Quirks.