Darren's surname seems likely to be Izzard. I can see why it's a bugger to anagram. Penelope's is trickier- all those consonants. I'm going to go for 'Whittern', as the most likely of an unlikely bunch of alternatives ('Penelope Threwtin', anyone?) Graham is indeed, I think, using a middle name. After a long blind alley in which I was convinced his surname was either Butler, I'm now going with 'Graham Paul Roberts' If Rosie is indeed named Hugh, his surname might be 'Stroude'. But from Dr Q's comment, I suspect s/he isn't. Maybe by 'sorta', Dr Q was hinting that the surname is Hugh, or more likely Hughes. But that leaves a pretty odd bunch of letters to make a first name out of- is there such a first name as 'Tudor'? Finally, I don't think Chalky's name is Kathryn, since we have the additional clue that spelt backwards it looks Russian. I therefore suggest she is that well-known Muscovite 'Yhtak Tropnevad', otherwise known as Kathy Davenport.
Jonathan Ellis? Hmmm... how about 'Jeans Hit Noll', 'Ah Jell in Snot', 'Halt Sloe Jinn', 'All Hens Joint'or even 'Anal Hens I Jolt'? I could go on, but I won't - I'll just point you here.