I'm sorry for your loss. It sounds like you are doing the very best you can for those babies and you will be in my thoughts. As already stated, no milk products. That could be what is causing the diarrhea. Diarrhea is very serious in guinea pigs - not to scare you - but it can be a life threatening situation especially with them being so young.
I'm really glad you are going to the vet again. I hope you can find a vet who is experienced with guinea pigs.
Pellet mash will work if you don't have Critical Care, but hopefully you can get critical care at the vet today. The babies need hay 24/7. It might be hard, but getting them eating solid foods as quick as possible is the best thing for them. Sometimes adding a little plain canned pumpkin into the critical care can make them want to eat it more. You need to be very careful if you are handfeeding young pups.
I highly, highly recommend that you go to
Guinea Lynx :: A Medical and Care Guide for Your Guinea Pig and post a thread about these babies. There is a lot of medical expertise there that you can learn from and they will help as much as they can. You can find out things to ask the vet and tips of things you can do for these babies. Here are a few links for you as well. Please let us know how the vet visit goes!
Guinea Lynx :: Hand Feeding Guinea Lynx :: Diarrhea
Are the babies in with the dad now? You can let them live with dad, so long as you get any female babies separate by the time they are 3 weeks old (well maybe 4 but we always say separate males from the mom by 3 weeks old to be safe - girls I think don't become possible to impregnate until 4 weeks old but I would have to check that to be positive). The dad could be a great source of support for the babies - showing them how to eat solid foods and drink from the water bottle.