I don't think you should do it that way. I would use square brackets, and write immediately afterwards: "(The comments within square brackets are mine.)" Square brackets have been used traditionally by writers to inserts their own comments.
Square Brackets [ ] | EnglishClub.com and others
You don't need to say the emphasis is yours if it occurs within square brackets - it's obviously yours.
If the third parenthetical phrase was the author's and you just emphasised it, you should leave it in round brackets, and after, write, "(The comments within square brackets and the emphasis are mine.)"
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