Here's an interesting discussion about Peter de Mauley father and son, sorting out some of the details of their lives.
https://groups.google.com/forum/?fromgroups=#!topic/soc.genealogy.m...
As a matter of some interest, it also shows that the number 4th and 5th were actually used for these two, and are not just a historian's invention.
Piers de Mauley, le Quart
Sir Piers de Mauley, 5th Lord Mauley