Hello,
I too tried to find the MacLellan family in the 1880 census and searched on ancestry and found nothing, except one family that is also researching the same family but didn't have a date of death only a birth year and place, Nova Scotia for Thomas's parents.

I would try and contact the St. George historical society to see if they have anything in their archives about a boating accident off the Tenant's Harbor shore in 1884.