Gem I suspect there are two wills! - one lodged in England pre move to IoM + remarriage and the 2nd made in IoM (and thus not known to English probate unless it was accepted by them in regard to disposal of English assets).
It looks to me that maybe John's siblings (+ any children by 1st wife) tried to prove (i.e. test) their English will in the Manx court but his 2nd wife proved her case and thus sworn executrix - you really need to get a copy of the Manx will (I'm off Island until end of next week + Museum library not open until next Weds)