Translation:My younger sibling's illness has already healed.
I think the simplest way and common way to say this in english is "My brother/sister has recovered." or "My brother/sister is feeling better now"
The illness/disease is not mentioned at all in this sentence, but normally people should come to their own conclusion that the "recovery" refers to an illness/disease that he/she had before the "recovery", so there is no need to include that word in the sentence.
When I feel forced to directly translate a sentence from another language into english word by word, then I think it actually ends up sounding awkward because each language has their own way of expressing things.
Then again I'm not a native english speaker, so if there are any better way to say it, I'm open to suggestions as well.
I think these kind of answers should also be allowed, but I'm not sure if everyone would agree because it doesn't exactly adhere to the rules of the game?