Occam’s Razor, of which I’m very fond, is a problem solving tool and not a law of logic. It gives a probable answer and not a definitive one.
In order to apply it in this case you have to know that none of the 25 other possible Jefferson males were at Monticello at the same times. Seeing as Jefferson was sociable and not a hermit, and that these 25 Jefferson males were family, Occam’s Razor argues that this is not so.
As nothing will be definitive we can just disagree.