Familysearch has a burial of a Thomas Etherington at Muggingotn 5 April 1829.
Probably the father?
There is a Thomas born to Thomas and Hannah 24 Feb 1782, and also a Thomas born to a Thomas and Mary 18 Jan 1789.
It looks as if you may be right that Thomas married Hannah first, who then died, perhaps after the birth of Thomas junior, (who probably also died), and he remarried her sister Mary. having another son Thomas.
Burial records seem to be very thin on the ground in the Muggington registers on famsearch and can't see these other deaths.
Also checked findmypast (if anybodyelse is looking), but they don't appear to have Muggington records at all. Nor does there seem to be a marriage licence for either of Thomas's marriages.
The burial record of Thomas in 1829, gives him born 1751 (it must say he was 78 years old in the burial register). Looking even more like Thomas the father.
No Etherington births in Muggington around that time, so looks as if they may have come there from somewhere else.
But there is a baptism of a Thomas Etherington 12 Jan 1755 at Ellastone, which is about 10 miles as the crow flies west of Muggington. Ellastone is in Staffordshire and Muggington in Derbyshire. The county boundary runs between them. Parents William Etherington and Rachel. A couple of siblings there too.
Worth looking at.
