Martha Dandrige married Daniel Parke Custis and bore him four children, two of which did not survive early childhood (Daniel and Frances died at ages three and four, respectively). John (called "Jacky") and Martha (called "Patsy") were with Martha when she married George in 1759 and were raised by them (Daniel Parke Custis died and left Martha a widow in 1757).
Patsy had epilepsy and died in 1773 as a result of a seizure. Jacky and his wife Eleanor had four surviving children but he unfortunately died of "camp fever" (probably typhus) while an aide to his stepfather, General Washington.
Two of Jacky's children then stayed with their grandparents at Mt Vernon (George Washington Parke Custis and Nelly Custis) and both of them lived long lives.
Very interesting post here Pharmboy. Thanks.