What is the most common familiar term to say "grandmother" or "grandfather" in a Puerto Rican home? I've read Yaya (o) is used, but then I read those terms mean vastly different (and negative) things on a different website.
In Spain we use yaya and yayo, they mean granny. In areas where we also speak Catalan, we use iaia and iaio, but, as Anemoah says, they aren't only used in Catalan areas. In Catalan, according to dictionaries, iaia comes from àvia (grandmother), said by little children, not from Greek, and iaio is the masculin form of iaia. So, in Puerto Rico, this word can come from Spain. I don't know any other European country where it's used.