"workhouse infirmary" suggests the hospital part of the set up.
So they could have been inmates, or could have lived elsewhere and just been admitted to the infirmary.
Where is the one that died in 1894 living in 1891? If they were still at home then it suggests that the one dying in 1881 was only admitted to hospital - there would have been no reason for them to have gone into the workhouse if they had a home and a spouse.