Fella on the right may be Sparse, although it is hard to tell. He wears a similar fedora (and has a pipe clenched in his teeth) in cover photo of his posthumous book of essays: An Honest Angler.
Sparse would have been in his late 50s in the early 1950s. (He died at 90 in 1983).
Photo could also be Ernest Schweibert...again, tough to get positive ID.
Some of the names of Hewitt's 'Neversink Rods' were: Dick Hunt, Rogers Lamont, Joe Bamford, George LaBranche, Tom Collins, Reg Cauchois, Steve Dawley, H.G. Pickering and Sparse Hackle. (This per an essay in The Legendary Neversink
.) Of course, there were almost certainly other guests, but these fellas sound like the core group.
Give a man a fly rod, a shotgun and a bird dog and he'll never be worth a d*mn.
-Old New England saying