I've got a scan of a family tree from 1666 that shows the following information:
Roger Beckwith (son of Marmaduke and Anne) had the following children by Dorothy Currer:
Anne, Grace, Barbara, Katherine, and Thomas
Roger Beckwith also had the following children by Susanna Brackenbury:
Arthur, Matthew, William, Juidth, Hesther, and Susan.
The only mention I have of another Marmaduke on this tree is the son of the above Arthur Beckwith and Marmaduke Wyvill, BUT the tree says that he died unmarried. Don't know if that helps or not, but that info is pretty accurate.