that Colonel Fitzwilliam is a second son. He is a younger son, but that description would not prevent his having more than one older brother - and possibly st least one younger, since he does not use the term youngest of himself. Elizabeth may be aware of his exact position, or she may be making a wrong assumption and he does not correct her because, having given his warning, he would want to leave the subject as quickly as possible. THe elder or eldest brother has, like his father, a bit of a name since as the heir to the Earldom of Dash he would be Viscount Blank. And as Colonel F is already about 30 the older Viscount may well be married and have children.