the whole story,
when the game starts in 1066 Godfrey III with the beard is duke of Lower Lorraine. He dies at 30/12/1069, the duchy of lower lorraine going to Godfrey IV the Hunchback,
Dirk V count of Holland plots an assassination (febr. 1076) on Godfrey IV the Hunchback, duke of Lower Lorraine (duke from 1069 on),
Godefroi de Bouillion is the son of Eustache de Boulogne and Ida. Ida is the sister of Godefroi the Hunchback.
Godefroi de Boullion becomes marquis of Antwerp in march 1076 and hopes to become duke of Lower Lorraine.
But he only gets the mark of Antwerp and King Heinrich IV promotes his 2 old son Koenraad to duke of Lower Lorraine.
in 1089 emperor Heinrich IV promotes Godefroi de Bouillon to duke of Lower Lorraine as he had helped Heinrich IV against the usurper Rudolf of Swaben, Godefroi succeeds Koenraad as duke of Lower Lorraine, Koenraad is Heinrich IV's son that is crowned king of Germany,
Godefroi de Bouillion was born in 1061 or 1062 so making him 5 or 4 years old when the game starts,
so bottomline is that Godefroi de Boulogne should be 5 years old and have a claim on the title of duke of Lower Lorraine.
so there should be a Godfrey III with the beard, a Godfrey IV the Hunchback and a Godfrey V of Bouillon,
However Godfrey III and IV should be called of the Ardennes (or d'Ardennes). Godfrey V 's house is refered to Bouillion/Boulogne but that can never be the same,
Other sources confirm Eustache - Godfrey V's father to be of the Boulogne house. Later on Godfrey V claims the castles of Bouillon and Verdun,
so history knows him as Godfrey (V) of Bouillion,
but when the game starts there should also be Godfrey III and Godfrey IV and they are clearly from the house "of Ardennes" or "d'Ardennes",
http://www.friesian.com/lorraine.htm#upper
to be honoust, I didn't check with the current set up -

o