Translation:Where are you from, Iain and Andrew?
à = the straightforward preposition "from/out of"
às (in this context) = the prepositional pronoun "from masculine it/him".
After (most) interrogatives, you use the masculine inflection of the relevant prepositional pronoun (because you do).
- bho –> Cò bhuaithe? (From who?)
- ri –> Cò ris (To who?)
- a/do –> Cò dha (For who?)
You also us "às" before the definite article, e.g:
"Tha mi às a' bhaile mhòr" = "I'm from the city"
But here, London has no definite article, so it's just plain old "à".