I'm sorry to hear about your nephew - you might like to consider:
Old Michael Deed #69
dated 2 nov 1717;john caine + ann als corlett obo son pat;elinr quayle obo dau joney(her fa dead);to marry before st thomas day at kk michl;Caines to give half land;elinr to give over + above joney's fa share 40s + bed etc;witt tho quayle x;jo caine x;court may 1718

Lib Vas May 1718 Ballanimade 34s 8d John Caine milnr 17s 4d Pat Caine his son 8s 8d the said Pat Caine is entered for half the above rent with his father by virtue of a contract bargain dated the 22 Nov 1717 lawfully confirmed Fine 20d

Will Ann Cain als Corlet
d 12 sep;dau elinor cain,margt quiggin als cain (her son wm);gch john cain,pat cain,joney cain;dau-i-law ann cain;son patk cain exec

Margt Cain married John Quiggin Michael 17080831 - ch margt,john,tho,wm,ellin,philip,patr + jony (some conjrctured as for a period Michael bapts did not give mothers name

Patrick Caine married Joney Quayle Michael 17171210 - ch John, Jony, patrick (again 2 conjectured as no mother;s name)

Jony Cain als quayle b'curleod bur Mic 17250123 - d 23 jan 1724;sis-i-law elinor;mo-i-law alive;bro-i-law wm;husb patk;unnamed ch ua uncles John + hugh Quayle;witt Tho Corlet x + Wm Quayle x both sick + dangerously ill by probate in Feb;

Lib Vas Michael May 1741 Ballanimade or Bargarrow - 34s 8d John Caine milner & Pat his son 17s 4d Pat cain 34s 8d pred John is dead and his son Patrick entered for the other half by vertue of his settlement of marriage dated the 22 Nov 1717 confirmed by the officers Fine 20s

in lib assed 1750 Pat Caine 17s 4d,under Ballanimade

1765 will Pat Cain - d 20 sep 1765;ballacurleod;dau ann,elinor,elizth exex;son patt

I can push John the miller back a generation or two - his father was also John the Miller I think buried 1717.

Don't forget the other Cain family was in ballaugh - your quoted will is from Michael - refers to a totally different family