Hi Sue,
Re Mark CHRISTIAN and Margaret KISSACK
As far as I can work out, Lewaigue is a place within Port E Vullen, which is a between Ramsey and Maughold.
You may have more information about this, but it means that the family may not have actually moved between the 1841 and 1851 Census, and it may be Mark’s Margaret in 1861Census (still at Lewaigue)
Can the Margaret CHRISTAIN of Pt-y-Vull age 64 who was buried 16 Apr 1860 be accounted for?
Apart from the age of Margaret being well out in the 1861 Census, everything adds up.
Will have a look over the new information you have just posted next.
Regards
Michele