Just declare the higher value & be done with it. It sounds like you know it could be more & are trying to figure out a way around it. If they ask you how you came by them, you mention the inheritance & odds are you're not going to get hit with a fee, or a minimal one. Or at least you can have the discussion in-person with them on the face vs market value. That's probably better than having them confiscated & then paying a penalty.

Cheers.