A few thoughts about this. Watch the spelling of "Joseph."
"Adores" is the right word here, but in my part of the world it wouldn't be used in casual conversation. It strikes me as rather formal.
"Idol" looks okay to me.
"Icon" doesn't work in this context. An icon used to be a religious symbol, specifically Russian, but lately the word has become very common, meaning a generally recognized symbol. For example, our CN Tower is often referred to as a "Toronto icon." I heard someone referred to as a "pop music icon." It's possible this usage isn't really new, but I'm hearing it continually now. I've also heard the adjective "iconic."
We have an idiom that would apply to Joseph's sister: "She worships the ground he walks on."
But this is used so much that it has become a cliche, and it's a good idea to avoid cliches.
Student or Learner