Orderic Vitalis, finally, records that Geoffrey was the one that inherited his father's possessions, suggesting that he was the oldest son.
This looks like an error from Orderic's part, as it was Serlo, not Geoffrey, that stayed in Normandy and inherited Tancred's possessions.
[3] In 1059 Geoffrey asked his younger brother, Robert Guiscard, to help him suppress a rebellion that arose in the region of “Tetium” (in Abruzzi).
[4] Goffredo Malaterra records that after taking the fortress of Guilmi, Geoffrey died in battle near Chieti.
[5] However, this information is not reliable as there were different counts named Geoffrey in that period, so we can't know for sure of which of these the chronicon is talking about.