I'm having some trouble understanding the meaning of phrases that uses two verb particles in two different words but with the same verb.
怠惰はあなたを不幸にする - Your laziness will make you unhappy.
する pointing to both あなた and 不幸.
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は(wa)is concatenated with 怠惰(taida).
を(wo)is concatenated with あなた(anata).
～にする(~ni suru) is concatenated with 不幸(fukou).
I don't think any other interpretation than this is possible.
Maybe you are confusing the fact that many expressions that end with <～にする＞ are already idioms themselves. So 「不幸にする」can be regarded as an idiom, so 「不幸をする」doesn't seem to make sense.
不幸だ is a na-adjective turned into an adverb using に, the same way －くis used to make adverbs out of i-adjectives. Do not mistake this に as the に particle, it is just the renyoukei (conjunctive form) of the copula だ.
It is also worth noting that にする can be used with adjectives much like になる, except the meaning is causative, as in to make something happen, rather than something just occurring or becoming that way.
All that said, the translation of your sentence is "Laziness makes you unhappy"