If you have access to a Mormon Family History Center, you can order the marriage film for a few dollars and can make a copy of the entry for @$.25.
Otherwise you can order from one of the IOM or British record repositories--this is more expensive.
It will be a parish entry and won't give much info beyond the date and place which was Braddan.
It would say if either had been married before (i.e. widower, widow), if either was of legal age, parish of residence.
Sometimes the witnesses are family members but often they are church personnel.

Likewise you can get the parish entries for the baptisms of John in Douglas, Lucy in German, and the children in Douglas.

I have this in my files.
1841 Census Index
Douglas 8 29 151
QUAY
John 40
Louisa 40
Manassah 4
William 15

1851
Douglas 55 Sand Street
John Quay head married 50 labourer b Douglas
Louisa wife married 40 b Douglas
Manasah son 14 b Douglas
John son 6 b Douglas

1861 Census Index
Douglas 4 268
QUAY
f (Lucy?) 53
Ann 16
John 60
John 12
Robert 8
Thomas 19