I can give some more information about William McKeown senior.
He was described as a soldier both in his son's marriage record in Jersey 1847, and his own death record on Jersey 1848.
He was b.c.1784 in Ireland, presumably the North given that surname, and married to Elizabeth, b.c.1800 and they are both on the Jersey 1841 census. There are mentions of Church of Ireland and Presbyterians in later records, so I don't think they were Catholics.
His first son stated that he was b. Cork c.1818, so was his father stationed there at that time? This seems unusual since I've read that the British Army discouraged soldiers from having wives and children (unless officers, and I have no reason to think he was that) and also that Irish soldiers were mostly sent abroad in case there was a revolt and they joined in on the wrong side !
His next recorded child was Margarite in Gibraltar c.1824, and there is a gap of 6 years there, so there might be 1 or 2 more there that I don't know about.
Then comes John McKeown b.c.1826; on the 1841 census it says b.Ireland, but in a newspaper report of his death on Jersey 1856 it calls him "of Gibraltar", but that may just mean that he previously came from there.
Next is James McKeown b.Woolwich Kent in 1828
Then Robert McKeown b. England c.1831 and I have just found a record in Tynemouth which may well be him, baptised to William and Elizabeth McKeown.
Lastly Mary Anne McKeown b. Jersey 1838
Hope this may mean something to somebody out there
Graham