You can use the phrase treat someone pleasantly.
Sentence 1 has a few errors though. In particular, the list of three items does not work because treat only applies to the first two items. The easiest solution is probably to delete the word gracefully because I don't see what it adds to the sentence (in that case, also delete the comma preceding gracefully). If you want to keep gracefully, one solution would be this:
Michael failed to treat his parents pleasantly[STRIKE],[/STRIKE] or gracefully and was unhelpful while they visited him.
For Sentence 2, the words and mannerism sound a little natural to me. I would just delete that part. And again there are a couple of other errors. You could fix the issues in this sentence in a few ways, but here is one idea:
I failed to show my boss the right attitude [STRIKE]and mannerism[/STRIKE] [STRIKE]towards my boss[/STRIKE], which [STRIKE]have[/STRIKE]has [STRIKE]formed[/STRIKE]made a lasting impression [STRIKE]in[/STRIKE]on him.
If you want to keep the part about mannerism, perhaps you could say "I failed to show my boss the right attitude and work habits, which has..."
Note that I switched from have to has because the word refers back to the act of failing. If you remove the idea of "fail" and used a different sentence, the word have might be needed (e.g., "My poor attitude and work habits have left a lasting impression on my boss.").
