"Where are you, Iain and Andrew?"
Translation:Càit a bheil sibh, Iain agus Anndra?
'Sibh' is used as subject and direct object: Tha sibh math. Tha mi a' faicinn sibh. 'Leibh' is one of the many instances of a pronoun combined with a preposition: le + sibh = leibh. aig + sibh = agaibh. air + sibh = oirbh and so on. So 'leibh' is used in expressions that employ 'le', such as 'Is toil le' (Literally 'it is pleasing with/to'). So 'you like' is in theory 'Is toil le sibh' which becomes 'Is toil leibh'.
I think that's how to explain it, but I stand to be corrected!