There is a death record for a Joseph Telford on Irish Genealogy (https://civilrecords.irishgenealogy.ie/
) in Clogher, County Tyrone. The informant is his wife Elizabeth, but perhaps this is a second marriage.
You also say that the other WikiTree researcher for this family is now deceased - are you sure of this? Perhaps you ought to report this to info at WikiTree so that it can be followed up.
The Ann Telford that died in 1882 was married to an Edward, and lived in Ballymena, County Antrim