I'm no expert on this family, but I have been researching them them lately. Dates of birth are pretty hard to come by during this period, so we have to work with what we know. We are fortunate that Bible records exist for Martha's brother, Benjamin II, giving his DOB as 27 Nov 1743. Also, we know that Rev. John LaPierre gave land to his dau Martha and her husband, Benjamin Fordham I, in Dec 1740. Making an educated guess, I would say this gift of land was around the time of their marriage, which is consistent with son Benjamin's DOB of 1743. Until other evidence emerges, I think we can reasonably conclude that siblings Abraham and Martha were born after 1740 and before 1760, mostly likely within the 1740s.
I have not found anything suggesting daughter Martha married Stephen Williams, but Martha's line has not been my focus. If you look at the trees out on ancestry.com, you will see that some people ALSO say that Martha, daughter of Benjamin Fordham and Mary Blackshear, married Stephen Williams. Now, I really haven't researched this to any extent, but there is a Stephen Williams in the records of Jones County, and those records (1790s into early 1800s) are consistent with a man who would have married the younger Martha Fordham.
I will say, in general, that I am suspicious of a lot of what is written about this family. For instance, I can't a single piece of evidence that Benjamin Fordham II married a Mary Blackshear. But at this point this "fact" seems to be cast in concrete. It is probably a good thing to question, as your have, what you find out on the internet.