There is a joint will for Thomas (he being dead) and Elizabeth Clague (the Claque form is an invention of the IGI) - in 1798 under German - however all it appears to mentions is property in Peel - at their marriage which took place at Kk Michael he was noted as of Peel and she of Kk Michael.
Thomas was I think buried German 17970604 but I can't find a burial for Elizabeth. Neither can I find any property in Peel under Thomas's name (the transfer of which might well mention any children) (see manxnotebook under peel)

The marriage of Mathew + Ann horne (both of German) had as witnesses charles cooper of peeltown, angus munn revenue officer - Horn is decidely not a manx name

I suspect Ann died pre 1786 (tho I can't see burial or will) as there is another marriage of a Mathew Cowin to widow Margaret Christian - his will is in 1789 (summary on MNB)