Your response prompted me to have a look at some of the original data re William and Mary Humphreys again,and it raised a number of queries in my mind,perhaps they will turn out to be what another person on this site memorably called"red herrings barking up the wrong tree":-
1.In the original intestacy bond where Mary Humphreys is described as sister,the date stamp says 1850.I could understand this in a will of somebody who died in 1852,but not an intestacy.
It does appear as if the William Humphreys born Llanaber 1803(parents William and Catherine),had a sister Mary born 1799.
2.You say that the children of William and Mary(unknown),i.e. William and Mary Anne are legitimately baptised,apearing in the parish registers.I have struggled to find them.Can you please confirm parish and years.
3.You have William marrying in Liverpool in 1861 to Ellen Vaughan(and fate unknown after that).
He is registered on the census(7th April 1861) with his mother in Merionethshire.The marriage is also April 1861-not impossible of course,but he would have to get his skates on(no maritime pun intended).
4.If I read your family tree correctly on Mundia,you have Mary Ann(e) staying single?
There is a marriage in 1860 in Llanaber of Mary Ann(e) Humphreys to William Davies.
Her father is given as William Humphreys( mariner).It does not say deceased.
They are probably the couple at census ref. 1871 5692 15 22
The witnesses are Jane Evans and John R Jones(same persons as on the original intestacy document?)
This Jane Evans may also marry a John Vaughan in 1860(haven't checked dates)-interesting with your Vaughan connection?
They may be the couple at census ref. 1871 5690 75 12
Regards
Roger