yes
money!
Yes they can and they have been
no
You will need a passport.
Yes, many do.
yes through paper work and then you are welcome to come to the us as a us citizen.
http://jhcuk.org/citizenship.asp From Lawz
Yes
Jamaica is part of the British Commonwealth, so most unlikely.
They are officially married. One spouse can sponsor the other for immigration to his or her country.
A Jamaican can join the US Army if they have a green card or they are a naturalized citizen.