This is them on 1871
Hannah Boffy 23 Bilston, Staffordshire, England Sister Wolverhampton Staffordshire
Thomas Jones 55 Brewood, Staffordshire, England Visitor Wolverhampton Staffordshire
Harriet Mears 39 Griesly, Leicestershire, England Wife Wolverhampton Staffordshire
Harriet Mears 15 Wolverhampton, Staffordshire, England Daughter Wolverhampton Staffordshire
James Mears 38 Appleton, Lancashire, England Head Wolverhampton Staffordshire
Mary Ann Mears 13 Wolverhampton, Staffordshire, England Daughter Wolverhampton
So from this all I can assume is that Hannah Boffy is James' sister, but she is listed as unmarried. I thought perhaps Boffy would be her married name? Don't know anything else I'm afraid.
If she was a widow it would say wouldn't it? Or do you think for some other reason they have different surnames?