Translation:Have you seen my brother with your brother?
Pretty much I believe, with gyda being Southern and efo/hefo being Northern.
Gareth King says in Modern Welsh: a comprehensive grammar:
Efo (in some areas hefo) is the general word for with in the N. In the S it is always replaced by gyda, a word which, in turn, is virtually unknown in the N (except in the set phrase gyda’r nos at night). The two words are not, however, exactly complementary - gyda (or ’da) is also used in the S to expression possession (see XXXVIII), but for this function the N uses not efo but gan° (see §455).