Uly, thank you for your comment but in the case the Russian "в" has the meaning the one who belongs to the family, so I think it's "of", isn't it?

No, Irina, in this case we use the preposition IN.

Everyone of family members who belongs to the family is one IN the family??? one not OF the family???👀

No, with ONE you always use OF when it means один из: everyone who belongs to the family is one of the members of the family.

Каждый в семье means one who belongs to the family. It's just another kind of expression. Everyone in the family would mean one at home...

It's interesting

Irina, everyone who belongs to the family = everyone in the family - regardless of whether they're at home or not.

I mean everyone in the family would mean in Rusdian one who is physically at home

Oh! Got it :)