"¿A ustedes les encanta correr?"
Translation:Do you love running?
This verb, like gustar, puts the thing being liked as the subject. The person who likes becomes an indirect object. This is just how Spanish phrases it.
Is this the standard 2nd person plural? Or is it the politness form? (Sorry for bad phrasing) I thought the normal 2nd person plural was 'vosotros'. But it hasn't shown up in any exercises yet.
That is because Duolingo teaches Latin American Spanish. In LatAm, the vosotros form is not used, but instead they use ustedes for any plural 2nd person. But if you are in Spain (or Equatorial Guinea, for that matter), the vosotros form is used as a familiar addressing, and ustedes is used for formal addressing.