18th: ROBSONs (mis)remembered?

Looking at the ROBSON connection, if any, between Isabella Sinton and her sister Margaret:
Margaret had her brother-in-law George Robson living with her and her husband Thomas Robson; George's death cert shows his parents as George Robson, carter, and Margaret m.s. Pertis, the informant being George's nephew, Richard Robson of Maisondieu.
Isabella's husband was Richard Robson, and they lived at Maisondieu.
This Richard Snr's death cert shows his parents as Thomas Robson, blacksmith and Margaret m.s. Pertis (the informant was Richard and Isabella's eldest son Thomas).
Am I looking for one woman with two husbands or simply two Robson brothers who cannot remember their grandfather's name and occupation?
If I go for the 2 out of 3 aint bad rule, I found that Margaret's husband Thomas also survived into civil registration and his dth cert shows his parents as Thomas Robson, blacksmith and Peggy m.s. Pertis, with Margaret being the informant.
Wonder if Pertis is actually Porteous?