NTA.

One of my good friends has a son named Sora because of Kingdom Hearts. He's 8 now, never had any issues with his name. Roxas is perfectly fine.

"We talked about it and he finally told me that he didn't want to fight
with his family over a name and that maybe it would be good if we picked
a more conventional one."
If you have a moment, I would recommend sitting down with your BF and talking about setting healthy boundaries with his family over the choices made for your baby. If he thinks letting up on this one issue means he won't have to fight with his family over the decisions you two make for your baby, he's in for a long road of rude surprises.