Fam he's a gaal.
We don't say ''AUN'' to gaals.
Only Muslims.
But RIP is alright.
How can he rest in peace. He is kafir.
What is awaiting the kufar is clear and Allah knows their individual situation.
And Noah called to his Lord and said, "My Lord, indeed my son is of my family; and indeed, Your promise is true; and You are the most just of judges!"
Hud:45-46
He said, "O Noah, indeed he is not of your family; indeed, he is [one whose] work was other than righteous, so ask Me not for that about which you have no knowledge. Indeed, I advise you, lest you be among the ignorant."
Even saying RIP is ignorance atleast if not a sin.