1of the 2 abandoned kittens I am caring for has the runs and won't really eat what can I do?

On Saturday we found 2 kittens, well found isn't really accurate they dropped out of my friends ceiling onto a blanket in her laundry room (thank goodness for procrastinating on laundry, right)! We checked the hole to see if there were more and if the mommy cat was still there but sadly no such luck. We took the 2 kittens to the vet and he told us to get kitten formula, keep them warm and that they were just a few days old if even that because they still had their umbilical cords attached. This has worked they were eating and urinating but not defecating so I asked what I could do to help with that and was told to rub their nether regions and tummies with a warm damp cloth. This has helped quite a bit they were doing really well.I now have another problem one is urinating more and defecate a bit but the other one while still urinating now seems to have the runs and will not really eat. I don't have the funds to go to the vet again and I need some guidance on what to do I don't want it to die and I am afraid that if one passes on then then the other will to and I really want both to live. They are very cute. They still have not opened their eyes and the one that doesn't have the runs is doing really well and eating great. I just need some suggestions on what I should do for the other one. Please if you have anything that might work let me know!