I’m sorry for the delayed response!
For Kaya Scodelario, since her brother on Skins was played by Nicholas Hoult, I would suggest Willa Holland. Another, younger female suggestion would be Dakota Fanning, who, though she has a different coloring, has a very similar face shape.
For brothers, I would suggest Freddie Highmore, who has a pretty wide age range, since he was a child actor and is eighteen now. For a brother on the older end of the spectrum, Jensen Ackles is a possibility, and he could play characters from early to late twenties, or early thirties. I hope one of these works for you!
Any more suggestions for Anonymous?
for siblings for kaya, i see a HUGE resemblance to emily didonato and logan lerman.
Willa Holland as a Kaya Scodelario sibling!
As for males, I’ll have to think a little more. XD
Siblings for Kaya Scodelario—
Lauren Cohan, Jensen Ackles, Nick Atkinson (from the band Rooster), Willa Holland, Ana Beatriz Barros, Evangeline Lilly, Taylor Cole, Marshall Allman, Nico Tortorella.