Well, we went to the vet's last night after the CP meeting to take them home. They have been on a drip since Saturday and are now rehydrated. Sadly that's about the only good news.
They are still not eating and are on convalescence food, syringe-fed every three hours. We made them beds and put them in the warm but Alfie kept crawling out of the catflap and lying on the wet, cold floor outside. He can barely walk, he's staggering around all over the place. He's lost so much weight.
I can't foster them as they still pose quite a threat to my cats so they are in isolation now. We sealed off the catflap and made them as comfortable as possible.
I got in very late last night and I am exhausted. If two cats can do this to me, just a volunteer who cleans and feeds once a week, it only adds to the respect I have for those of you who go it alone and have this sort of thing to deal with regularly.
I'll update you when I know more