I may be a medievalist, but I'm nonetheless very much up for puns
I think the thing you might struggle with is finding enough well-known knightly/legendary names to pun on, since surnames were not always used and/or were often place based in both the Arthurian legends and the real medieval period generally. We might get 16 though...
I'm not sure I'd use Bannister as it's
a real surname. I very much like birodragon.
Other names one could use as a pun basis...
de Montfort (Led 2nd Barons War)
Plantagenet (English royal house)
Fitzwalter (Led 1st Barons War)
Bruce (as in Robert the Bruce)
Wallace (ol' William)
Hauteville (Norman family who conquered Sicily)
Neville (Surname of the earl of Warwick known as "the Kingmaker")
Glyndŵr (Leader of the main Welsh rebellion in the Middle Ages)
du Lac (most often used as Lancelot's surname)
Aurelianus (given as the surname of the predecessor to the Pendragons)
da Hammo (the surname of Tolkien's eponymous hero in the book
Farmer Giles of Ham, who becomes King after some shenanigans with a dragon and a blunderbuss).
le Fay (Morgana's surname)
Roncevaux (not actually a surname, but the battle in which Roland famously died)
Díaz de Vivar (El Cid's real surname)
Campeador ("Great Warrior", a nickname of El Cid)
Cid (See previous two suggestions)
Martel ("the Hammer", a nickname of Charlemagne's grandfather)
> Plus the GoT house names
I guess the question is whether a list like that is well known enough to work with, which isn't a question I know the answer to.
Out of interest, where did you find the name Benwick attached to Lancelot? It's not one I've seen before in any of the Arthurian variants I know...