My Mountenay family. (sometimes written as Mountain or Mounteney)

Research at Ancestry.com gives the following:
Benjamin Mountenay born 1758 Morton, Nottinghamshire, died 1840, married Anne Welch 23 October 1781 Blesby, Nottinghamshire.

They have at least 4 children:

Thomas ? baptism record gives baptism date 29 May 1785 - parents Benjamin and Ann
Benjamin ? baptism record gives baptism date 19 November 1788 - parents Benjamin and Ann
John ? born about 1786, died 1862
William ? born about 1791

In censuses, Thomas and John have both been listed as being a tailor.

My interest is in John, my 5th great-grandfather and his descendents. There are a couple of possible marriages, both to women called Sarah, both in different years/places.
He has several children, most of whom appear to have been born in Guildford. The mystery for me is that his eldest child (that I can find) Sarah Ann, was born in Dublin, Ireland. I cannot understand why, unless he was visiting there and maybe married an Irish woman. Sarah Ann married Jacob Hook (my 4th great grandparents) 10 October 1829. In 1841 and 1851 censuses, they were living with her uncle Thomas. Does anyone have any ideas?

1841 census:
John Mounteney, aged 55, tailor, not born in county
Sarah Mounteney, aged 50
Maria Mounteney, aged 25
Eliza Sedgman, aged 20
Emma Mountenay, aged 15
Charles Mountenay, aged 13
Frederick Mountenay, aged 9
Edward Mountenay, aged 2 [grandchild, son of Maria]
John Buglear, aged 1, not born in county [grandchild, son of Frances ? not here at the time]

Jacob Hook, 35 yrs old, agricultural labourer, born in county.
Sarah Hook, 25 yrs old, not born in county.
Charles Hook, 9 yrs old, born in county.
Samuel Hook, 6 yrs old, born in county.
Sarah Hook, 1 yr old, born in county.
Thomas Mountenay, 55 yrs old, tailor, born in county.
George Braid, 25 yrs old, [illegible], born in county.

1851 census
Thomas Mountney, aged 66, tailor, born Blesby, Nottinghamshire.
Jacob Hook, aged 51, nephew, labourer, born in Chilworth, Surrey
Sarah A Hook, aged 39, niece, born Dublin, Ireland
Charles Hook, aged 20, grandnephew, labourer, born in Thalpue, Surrey
Samuel Hook, aged 16, grandnephew, baker, born in Guildford, Surrey
Sarah S Hook, aged 12, grandniece, scholar, born in Guildford, Surrey
Fanny Hook, aged 10, grandniece, scholar, born in Guildford, Surrey
John Hook, aged 5 grandnephew, scholar, born in Guildford, Surrey


John Menntney aged 68, head, widower, tailor, born in Fiskerton, Nottinghamshire
Maria Menntney, aged 35, daughter, unmarried, born in Shalford, Surrey
Jane Menntney, aged 32, daughter, unmarried, dressmaker(?) born in Stoke, Surrey [married to Dewhurst Harrison]
Fredk Menntney, aged 18, son, unmarried, tailor(?) born in Stoke, Surrey
Ed B Menntney, aged 11, grandson, born in Stoke, Surrey
Eleanor Menntney, aged 7, granddaughter, born in Stoke, Surrey [real surname Harrison]
Dewham [Dewhurst] Mennteny, aged 4, grandson, born in Stoke, Surrey [real surname Harrison]