They do lewd things but it's more like they're using each other to masturbate.

Sometimes they fight too.

I'm off my period so lick mine too~

Oh, all right, fine~

You're getting too cocky, Maare!

Don't pull on it~!

Maaru,

do the thing where you put your peepee inside~

You mean sex.

Yeah, sesk...

No, sex!

Maare likes to be spoiled. Maaru is a bit of a bully but a good big brother.