Rendre visite + aux

Jim's right. Since aux is grammatically à + les, you can't have à les mes parents. That's grammatical nonsense. But you could have, e.g.,

Je rendre visite aux parents de ma petite amie. -- I visit my girlfriend's parents.

Bonjour Jean,

Aux --> à les

You ask why not       "Je rends visite aux mes parents" ?

1) Let's rewrite the above including your proposal  "Je rends visite à les (aux) mes parents"

2) Let's now drop "mes"  leaving only "aux"   -- whose parents?  Immediately there is an ambiguity introduced.

The term is "rendre visit à"  --> aller voir qqn

Hope this helps clarify the grammar for you.

Bonne Journée

Jim