YTA

Sure, they don’t own the name. Neither do you. The fact of the matter is, you and your husband poached the name from your BIL and SIL after they experienced something incredibly traumatic. It means something to SIL as it’s from her favorite ballet, and it means a whole hell of a lot to both of them because THEY chose it for their unborn baby.

You and your husband have no compassion or empathy. You come off as very self-centered and egotistical. Your husband is giving off golden-child vibes. What you are both doing to your BIL and SIL is disgusting. Imagine stealing a dead babies name from your sibling, knowing hearing that name will forever cause unimaginable pain, and not only sticking to your decision but doubling down and blaming them for the pain YOU are inflicting? As if YOU have the right?

Do one nice thing in your life and either pick a different name or get out of their lives because they’re too good for you and your husband.

P.S. BIL isn’t jealous. He’s been kicked around and been an after thought his whole life. It’s not jealousy. It’s trauma and anger.