Where and when did this couple live and marry? What religion were they? How common was/were the surname(s) in their community/communities?
There are several cases of: spouses with same surnames; with same surname as mother-in-law's maiden name; cousins marrying probable cousins over several generations; brother and sister of one family possibly marrying sister and brother from another, sometimes possibly related family in my maternal GM's maternal lines. (Her paternal line was Irish so they probably did the same.) I don't know if and how the various spouses were related to each other prior to marriage. One line lived in a small town/large village, (pop. about 1200) which was off the beaten track until late 18thC. The other lived in a rural area. Both surnames were locally common, one was distinctive, and the families had been established in their districts since medieval times. They were all Catholic except one husband, so baptism, marriage and burial records are incomplete. The "town" families are listed in their households on 1767 Return of Papists. One family were yeomen and had their own businesses and are well-documented in the way of wills, leases, marriage bonds, poll books, newspapers, and even a contemporary book and a historical society journal from 100 years ago. Even with all that, I'm not sure who was who. The other family were ag. labs. so didn't leave an extensive paper trail. Both families suffered from a dire shortage of male forenames. One had a surfeit of females called Elizabeth or Jane.
I've wondered what DNA would show.