I'm happy that things are looking better for these two little ones. I have to say as well that the more I hear about your Vet's proactive stance, the more relieved I feel.
I'll mention one thing about the "eating litter thing"...it may mean nothing,as there can be several reasons (most innocuous), but sometimes it can indicate a low red blood cell count - the cat bordering on or being anemic. If that were the case, there would be other signs as well...low or lower energy level, lethargic, pale (less pink, more whitish) gums, cooler body temperature. These are all things you should monitor.
FeLV+ kitties have a very special meaning for me - I lost a very special little one - not to the Feluk but, to the incompetence of a Vet and to my own ignorance of even the most basic of rules, to get a second opinion. This was all before I learned about the wealth of information and supports available via the Web.
One thing I've learned since, something I would do now if I were to face this again and something I would urge you to at least consider is to join a group of people whose focus is the management of their FeLV kitties health. You can find them here
http://pets.groups.yahoo.com/group/FeLVPositiveCats/