You can't just switch them from sheep's milk to cow's milk, they time need to adapt. Feed a bit of calves milk mixed into one feed for a few days - add some probiotic yoghurt too, I would - then add it into another feed for a couple of days, then half and half for a few days, then try them on all calves' milk. And be aware that once their systems are used to 100% cows' milk, they would need the same gradual introduction to go back to ewes' milk.
However, swapping them onto powdered calf milk - which is probably just about as unlike fresh, raw Jersey milk as it is ewes' milk! - when they're already compromised doesn't sound very sensible to me, sorry.
I would put both of them on Pfizer Scour Formula for 24 hours to clear their systems, address any scouring, and give them then minerals, vitamins and electrolytes they need. You can keep them on that for 48 hours if you need to, which will give you time to find a neighbour who has some lamb milk left over
. Or to get a new, small bag; you can keep what you don't use till next year, if you keep it well sealed up.