Thanks everyone - and yes, clare, definitely worth the wait!
They are still putting on weight and eat like they havn't had food in ages. I have to be careful about how much I give them as they will eat everything on offer in about 5 minutes and I don't think they would stop if they got full. I think this could be something to do with their past home but I don't know enough about it really, just how skinny they were when I first saw them.
They also do a wierd thing with towels, I noticed them doing it in the rescue and I thought its just a comfort thing, I sat down after a shower with a towel round me and they both jumped up and started doing it again. What they will do is knead the towel with their paws and claws and lick it, the towel they had in the rescue centre was very soggy at one corner.