The RS shouldn't prevent sanji frim using DJ, even if it's fire proof.
The problem with sora being a lunaria is that all/some of the vinsmoke children should inherit the pyromancy, but no one did, also if fire wasn't modified into sanji's dna, what ability he was supposed to have in the first place?
If king was the model for what a lunarian should look like, then why none of the vinsmokes have wings?...