I can see how it makes sense for your characters IC, and that's all to the good...and as your realm seems to be one that has no problem with one family holding multiple positions (or individuals holding them) then I guess it's cool.
Personally, I don't really dig realms like that. While it can be a fun to play nobles who want to hoard all the power, if you're not one of the people who have it, things can be pretty dull. While it might be more artificial to limit the number of positions one noble or noble family can have, it seems more in keeping with the idea of sitting around playing games at a friend's house.
