Today I looked up the Church where Mr. Bishop erected a monument.They do not respond to letters, email, etc. for genealogy but will provide information in person.Since I am not anywhere near VA and can't get there at this point in may life--maybe someone who lives near Augusta Co VA could visit the church to see if they have a record of whether Robert was married to Elizabeth Preston or Elizabeth Renix/Rennick. I also don't have the money to pay someone to do it, but that is another option.
Another option is to see if there are marriage records in Ireland.
Another option is to try to find the records used to compile the book "Descendants of Robert and John Poage".Hopefully someone still has them somewhere
If anyone does find something, please let us all know.