Welcome, Arch!
Probably isn't any website that says it, it is a rather obscure bit of trivia. Plus, you have the nicknames slightly wrong. In Warnie's diaries, for a period in the 1920s, he refers to himself as APB, for 'Archpigibotian', and his brother as SPB, which he never defines, thought 'Smallpigibotian' is probably a fair guess (but, still only a guess). The two in letters to each other refered to their youthful attitude towards life as 'pigiebotianism'. If you can find a copy, you can get the full details in Brothers and Friends: The Diaries of Major Warren Hamilton Lewis.
Hope this helps.
Selah,
Sven