Thomas Oldfield who married Isabel Halsal was noted as a private in the 58th Regt of Foot (he was one of 3 privates of that regt who married in Peel between July to Sept 1784.
a Cath Oldfield was confirmed at Peel 1803, a Thomas Oldfield confirmed in Peel 1799 (normally confirmations were after 14th birthday ) Thomas junr has a gravestone at old St Germans (centre of Peel) noting died 9 Aug 1800 age 15;
Father Thomas was a corporal in the Northern Manks Volunteers from 1803
I have notes of 9 children - burial of Thomas junr as above of William in 1803 - there are possibly twins Robert & James but both names are repeated in later years but can't see any burials.
The family does not appear to be in either the Peel or Kk German lists of households of 1814