I am glad to get your rmail. I suspect that you are a Nixon and there is a boook about the Nixon family which I will check for anything relevant.
Now back to Harper. What you have is similar to what I have except i have William brother of Robert m to AgnesClark. I am not sure where you got your info but it is similar to what I posted at Ancestry.
The children of Lowdy are pure guesswork - same place, same time. There is a Lowdy Jr of which we have no further record and YDNA tells us that Lowdy might have had a brother who was the father of one or more of presumed children of Lowdy. If you snd me your email address,I can send a file with this info. Check the harper DNA results at www.familytreedna.com/public/harper
and look at subgroup R1a1. Cheers Mike Harper (email@example.com