Welcome to the forum.

Either one or both are suitable to be restored. I'd eventually do both, especially being heirlooms, for the reason Moonshae mentioned.

Either will shave well with a good edge put on them as both Sheffield and Solingen made excellent razors. In use there is not much difference between a 5/8 and an 11/16 sized razor. When Barbers were using straights to shave customers with I'd bet the razors they used were that size. It was all that was needed to do the job well.

Enjoy your razors once they are done up.

Bob