It isn't unknown for people to appear in two different places on census, but I agree that Robert and Martha are not your couple for reasons given upthread.
There is a marriage of a Robert Hamilton to Margaret Howie in 1881 on Scotland's People. Unfortunately that is a pay per view site and you need to buy credits to see the certificate.
OC
There is a marriage of a Robert Hamilton to Margaret Howie in 1881 on Scotland's People. Unfortunately that is a pay per view site and you need to buy credits to see the certificate.
OC
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