Take a look at the dual readout V meter from Seadog.
https://sea-dog.com/groups/3992-dual-round-voltmeter
It's small and round so easily installed.
Also Amazon offers many units, some of them dual. Catch is they tend to be rectangular although small.
If you don't have to have them right in front of you or on a MFD display then they would be possibilities. Just fuse them all.