What does Fidelity say?
If Fidelity can’t do it for some reason you could have one of you gift all of the assets in kind to the other and close the empty account.
The unlimited marital deduction is a provision in the U.S. Federal Estate and Gift Tax Law that allows an individual to transfer an unrestricted amount of assets to their spouse at any time, including at the death of the transferor, free from tax.
