Good quiz idea. You could accept things like "pound coin" as well; that's the normal name for that coin. I tried "thruppence" as well, but maybe adding all those kind of words would be going too far.
Two Shillings should I think be accepted for the Florin as that's what they had written on them, at least the most recently minted ones did, see 1947 for example. Great quiz though!
The dates for the first £2 coin are wrong. Also, accepting two pound should be fine as it's a two pound coin. Or at the very least indeed accept two pound coin, didn't know what else to try, the forced plural is weird
And we use the word 'quarter' in the UK rather than 'fourth' for fractions - quarter should be accepted as well.
50p changed in 1997
10p changed in 1992
5p changed in 1990