Not putting any bets on my memory, but thinking I remember Thomas talking about some brothers that dear old dad had killed because they where eyeing his throne. As for his sisters, Daddy Raith broke each to varies degrees, so they were a bit safer. Which makes a little sense, since a pregnant daughter is easier to keep watch for, which a son could be creating a army (*) of his own children behind your back.
(*) When I say army, I'm more talking alike 6 to 10 white court vamps even if it did take twenty years to do so.