Oh dear God C., I am so sorry. I know how hard it is when one has a stomach virus, but 2 simultaneously has to be impossible, especially at 8 months old.
There isn't much you can do about to treat the vomiting and diarrhea but if they have been vomiting for 4 days you should consult your pediatrician immediately. Dehydration is the biggest risk with stomach viruses. Call the doc now!
Runny noses and congestion are much easier to handle. Saline nose drops, clearing nose with nose bulb, cool mist humidifier with a vicks methol strip (the kind you plug into an outlet) simultaneously in a room with door closed while they sleep.
I really truly hope that they are feeling better soon. My best to you!