I suspect you are placeing too much trust in the general DNA analysis - the Manx always had something of a reputation for clannishness (quote re the Cleveland (Ohio) Manx that they married within their Manx friends etc even unto the 5th generation) - on Island there were a restricted number of marriage partners and you would expect much shareing of genetic markers - what surprised me re the family was not the names but the pan-Island links which is relatively unusual.

I will try to dig out the wills of John Cain + also that of Margt Roney als Cain als Cannell when in Museum tomorrow (if not it will be a month or so later) however in the CTD sale mention is made of other land which I don't recognise the names - this may provide a link to the Cains tho if the bur rec is correct he came from Douglas area to Rushen a little before his marriage