Eoin and
OwenFrederic,
Fredrick,
Frederick,
Fredrik,
FrederikWallace and
WallisNathanael and
NathanielAllen and
AlanRaul and
RaoulMark and
MarcLuke and
LucCedric and Cedrick
George and
JorgeWesley and
Westley (sound just about the same out loud)
Victor and
ViktorThelonius and Thelonious
Stuart and
StewartStephen and
StevenChristian and
KristianLaurence and
LawrenceElliot and
EliotFinley and
FinlayEric and
ErikConnor and
ConorCarl and
KarlAlistair and
Alastair
If your friends are so intent on doing this, it might be wise if they chose a name that lends itself to more than one nn, just to simplify things.