All lovely names! To avoid Fred/Freddy with Frederick, maybe you could call him Ricky? And if you’re not fond of Ben for Benedict perhaps you could use Beck?
Some other ideas:
Cassian/Cassius - Cash/Cas
Laurence - Laurie/Lance
Percival - Percy/Val
Nathaniel - Nate
Charles/Charlton - Charlie
Raphael - Rafe
Vincent - Vinny/Vince
Roderick - Roddy/Ricky
Ambrose - Bram
Montgomery - Monty
Bartholomew - Bart/Ollie
Leopold - Leo
Desmond - Des
Lysander - Ander