We corresponded by email last November when you posted your query about Robert McCaslin. We had both come to the conclusion that Robert was the son of James W. McCaslin and Sarah Martin, and the grandson of Thomas G. McCaslin and Sarah Robinson, but there is only circumstantial evidence.
I have just found another circumstantial piece to add to the puzzle. In the 1860 Bond Co. IL census in the household of William R. McCaslin (also a son of Thos. G.) there are two Georges. The younger George (age 4) is George Emory McCaslin and is listed first. He also shows up in later census records with the family sometimes as George, sometimes as Emory. I have never been able to decide where George (age 8), who is listed last, belonged.
In the 1920 Bond Co. census Louis/Lewis McCaslin, son of Robert, has enumerated with his family a George McCaslin who is listed as an uncle. That would make him Robert’s brother. One away is Robert with wife and son. This would make three children for James W. and Sarah; George, Mary Jane, and Robert.
In 1860 Mary Jane is with Grandma McCaslin who is one family away from William R. Now we can surmise that the extra George is probably her older brother. Can Robert be far away?In 1870 Grandma has died and Mary Jane is with William R.but now both George and Robert are missing.The hunt continues.