Advantage to Unskilled

How do you handle situations where a character gets advantage dice to a skill they don’t have? I’m thinking here of a wizard casting Chameleon but who doesn’t have Stealthy; same thing for an elf casting Threne of the Chameleon.

I give them the Advantage dice, but they still roll their dice at double obstacle because they’re using Beginner’s Luck.

Same here.

Thing is, I always feel odd doubling the successes on a vs roll… and I use a LOT of them.