I doubt that Randy descends from Mark, since Mark's family left the Ohio River valley shortly after 1830.But you and Randy can surely learn more about his family.
The first place to look for information is to talk to or write to any living relatives.Relatives and other people that Randy's father grew up with could probably tell him a lot.
The second important place to look is in the documents that our governments keep about us.There is probably information about Randy's family in the papers that the military keep about his father's military service.If Randy can find where he was born, he can send for a birth certificate; that probably names his parents and tells where they were born.He can then send for his parents' birth certificates to learn his grandparents names and where they were born.
Another possibility is to look for obituaries in newspapers.An obituary in his father's home town may name not just his parents, but also many other relatives.The home town public library probably has copies of their newspapers on microfilm; a librarian would be happy to show you how to work their microfilm reading machine.
It certainly does seem strange to know so little about family.My own father did not know his grandmother's name and did not know that several family friends were his mother's relatives.An early death certainly can cut the link to a family's past.