I thought one generally made medlar jelly with bletted medlars, to get that particular medlar flavour, hence picking them in mid Autumn. Though one recipe I saw suggested keeping the medlars in a bowl for some days to soften if they hadn't bletted on the tree. Either way, picking them now seems very early - you wouldn't pick your Bramleys now to turn into jelly would you, even if they had enlarged.

Surely the "leaves" are the flower sepals, having an unusual persistence: just the same thing as one sees blackened around the arse end of an apple, but on a larger scale and staying green for longer.