The Celtic languages used 'Mac' for 'son of'. The system falls apart for Macbeth who was the son of Findláech mac Ruaidrí. Mac Bethad was called that as Gaelic for 'son of life' and Mac Findláech follows it as his full name.
Daughters rarely ever get mentioned in chronicles but the Norse gave their daughters the last name of 'daughter of'. The Romans did not even give their girls their own name; they simply gave a girl the father's gens or clan name feminized. Therefore Gaius Julius Caesar's daughter was called Julia and, if he had two daughters, they would both be Julia but one would be Julia Prima (Julia the First) and Julia Secunda (Julia the Second). Then, with all the women in one family sharing one name, there would be confusion so sometimes the elder would be Julia Maior (Julia the Elder) and Julia Minor (Julia the Younger).
Men in a family often shared a name too, witness the number of Tancreds in Bohemond's family. Bohemond was one of the lucky few who got his own name (a nickname because of his size) which makes him stand out in the histories.
Anyway, Wolf Hall is not about Fitzroy. It is about Thomas Cromwell, whose nephew, Richard, was the great grandfather of the dreaded Puritan reformer Oliver Cromwell. (Richard is in the story, which is why I thought of Oliver at all.) Wolf Hall was the home of the Seymours not the Cromwells or even the Boleyns, with whom the story seems chiefly concerned. When I reach the end, I will hopefully understand why the author gave the book this particular name.