Thank you for your notes, and all your work on this--I'll try to address as much of it as I can.
I've been very forgiving on spellings and places; Craine/Crain/Crane and Cannell/Cunnell for example, and I figure many people wouldn't make the distinction between England/British Isles/Isle of Man if they're just filling out passenger manifests or logging hundreds of names on a census. The family information I have (stories passed down and notes made on photographs all state Isle of Man, and I don't think it's a location you'd pick at random).
A family story is that Hector left New York to avoid a marriage he didn't want; the flip side of that is that he left New York to engage in a marriage that wasn't approved. Either way, I think that's how he wound up in New Orleans (his elder brother Jesse was already there). How Mary Ann got there is an unanswered question (was she already there and they met, or did they meet in New York and run away together?).
Hector died in Hunt County, Texas, around 1865. He had served for a short time in the 16th Texas Calvary (dismounted), a Confederate unit. He was killed "on account of his Northern sympathies". There's a newspaper story (actually a reprint of an earlier story from the early 1900s) which goes into more detail. Side note: Hector enlisted with a Media White; Media stayed with the unit for duration of the war. Hector's son William and Media's daughter Mary Jane married in 1867. I'd love to know the family dynamics on that relationship.
Hector and Mary Ann had five children: William C (my 2d great-grandfather), Rebecca A, M Elizabeth, Frances Louvenia, and John C. I have death certificates on the daughters--the one for Frances is where I got Mary Ann's surname. William C died in 1872 in Texas and I have not located any death record for him. John C probably died around 1916 in either Alabama or Mississippi, and I've had no luck with him, either. I also haven't found out what their middle initial stands for (I'm really hoping it's Craine...).
I've found some of the census records you mentioned, but nothing's panned out yet.
I did locate a John Craine who was investigated as a possible subversive in the Civil War. He was being held in a military hospital in Virginia, claimed to be a British subject with no intention of becoming an American citizen. There's no other biographical information on him, so that's kind of a dead end for now.
Finally, I treat anything from Ancestry family trees with great suspicion!