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You and your husband can take the child on a cruise with the mother's consent, without having your son's parental rights
terminated. If he already has a passport, he can use it for the cruise. If he doesn't, your daughter-in-law could go to the jail and ask him to sign consent forms to get a passport for the child. The consent form has to be notarized. If it is impossible for the mother to get a notarized statement from the father while he is in jail, she can fill out an affidavit swearing to why the father's consent may not be obtained.
Alternatively, if the ship sails from and returns to the same U.S. port, your grandson can travel with you with only a copy of his birth certificate, which may make things significantly easier on everyone involved. http://disneycruise.disney.go.com/planning-center/planning-library/travel-documentation-bahamian-caribbean/
It could also help to have a notarized signed statement of consent from the mother, along with a temporary POA allowing you to make medical decisions for the child, if necessary. This site has a sample.
There is unfortunately nothing in the law that would allow you to obtain a divorce or terminate your son's parental rights over the mother's objections. But if the purpose for wanting to do that is only so you can take your grandson on the cruise, that can be accomplished without terminating his rights.
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