Nephews or cousins? Wiki seems to think that the wives of Tancred d'Hauteville may have been daughters of Richard I, which would make them nephews of Richard II ('the Good') and cousins of Robert ('the Magnificent'), yeah?
In any case, it's difficult, given the d'Hauteville's limited powerbase (which prompted the exodus to Italy in OTL) and the panoply of other, better situated claimants- depending on the POD you have Bretons descended from Hawise (daughter of Richard I); Counts of Eu (illegitimate progeny of Richard I); Counts of Evreux (descended from Richard I's second son Robert Archbishop of Rouen); Counts of Burgundy descended from Alice (daughter of Richard II) etc.
I think they were cousins of Robert, but I can't be sure. I originally said nephews but I made a mistake on that.
I admit this is an hard case but see this scenario.
First lets admite that both wives of Tancred were related to the Ducal family, and that everything goes as per OTL until the Battle of Civitate.
The battle ends as in OTL, and in the end Pope Leo buys is freedom by agreeing to legitimatize Normand rule in southern Italy and to agreeing to name one of them as the true heir of Normandy, on the grounds of William being a bastard.
Now this is a very unlikely scenario, but it as some points in his favor. For what I could gather the Pope, at the time, and the Normand Duke weren't on the best of terms and in 1053 Geoffrey de Montbray is, I think, in Rome and can be brought to the de Hauteville side.
Now Humphrey might do this as a way to take Robert out of the way in Italy, to ensure that his sons succeed him.
Now Robert has the cunning, martial ability and the money to put himself as Duke.
I know that this is a very unlikely scenario, but lets think that everything goes alright to de Hauteville. What would be the repercussions of them being in command of Normandy when Edward the Confessor dies?