To clarify the intent of the line I wrote, Francel is reflecting on his status as the fourth-born son, as daughters are often excluded from the line of succession in Ishgardian houses (there are exceptions, of course).
The birth order of Count Baurendouin de Haillenarte's children is as follows:
Stephanivien - firstborn son
Chlodebaimt - third-born son
Laniaitte - firstborn daughter
Francel - fourth-born son
I realize this may beg an obvious question, but before you think to ask─no, I can't tell you anything about the second-born son at this time. Terribly sorry about that.
Hope that clears things up!