A lot of what you have learned through oral tradition matches with the old records, but some differs.
Thomas Keith Falconer gave a parcel of 100 acres on 3 Nov. 1798 to John Craskell Falconer, his "reputed" son, and George Ann Falconer. On 9 April 1804, Thomas Keith Falconer settled 50 acres on Sarah Powell, next to John Craskell Falconer'ssettlement.This was in the Brownshill Mountains.On her death, the land was to devolve to her "reputed" children by Nicholas Bent.At this point John Craskell Falconer was about six years old.Thus it looks like the gift of land to Sarah Powell was so that she would support and raise John.
The St.Elizabeth parish register shows that he had children with Susannah Eleanor Bent, daughter of John Bent and Anne Rochester, between 1802 and about 1808.Susannah was born in 1785 and died in 1831.In her will, she left most of her property to John Craskell Falconer and his "reputed" children by Dorothy Bent.She also mentioned her other children (Thomas Keith Falconer, Joseph Christopher Falconer, Richard AshmanFalconer, Ann Elizabeth Gordon, and Mary Caroline Ebanks).Mary Caroline Ebanks was her daughter by a later man.
John Craskell took Dorothy Bent as wife about 1818.On 15 Oct. 1818, he sold his 100 acres to Henry Cerf.On 15 Jan. 1819, he purchased 115 acres from Henry Cerf (this was in Queensbury). On 14 Feb. 1833, he sold this land to Dorothy Bent.They were legally married on 24 Dec. 1836.
Dorothy Bent was the quadroon daughter of Nicholas Bent and Sarah Powell.So the tradition of John and Dorothy (not Abigail) being brother and sister is sort of correct---they were foster brother and sister, being raised in the same household.
I haven't found that there were any descendants of Thomas Keith Falconer's children by Susannah Bent, except Ann Elizabeth, who married Larckin Gordon.
John C. Falconer is described as "mestee," meaning one-eighth African. His unknown mother must have been one-fourth African.I've seen the name Craskell in Jamaican records, but he could have been named for a friend.
Sarah Powell must have belonged to the same family as that of Colin Powell, but I haven't identified her.
There must have been a lot of disputes, like you said, and all the details you wrote fill out the story.There is no record of Thomas Keith Falconer's death (which must have occurred around 1808-1810) in Jamaica, so it is possible he died elsewhere.