Mostly the Welsh didn't use hereditary surnames, just patronymics. So this is shorthand for
Nest ferch Caradoc
daughter of Caradoc ap Madoc
son of Madoc ap Idnerth (Iorwerth?)
son of Idnerth ap Cadwgan
son of Cadwgan ap Elystan
son of Elystan Gloddrydd
When they run out of steam they often stick a nickname on the end.
Of course this makes it very difficult to talk about the Family of Morgan from the year 1089.
If Nest had a brother, he could have male-line descendants called Evans, Williams, Jones, Roberts, Davies, Thomas etc. And so could everybody else.