What Jan said.
Some breeders/sellers will keep meticulous records of vaccination protocols, some do not keep anything on paper at all and then some, will claim "Yeah, they've had all their shots" when reality is they have never seen a needle or nasal in their lives. I vaccinate everything that comes here, regardless of what the seller says. The calves may have been fine when you bought them, but that doesn't mean they stayed that way thru transit. There's lots of evidence that some of these bacterial pathogens are very long lived in dormancy, and a dirty floored stock trailer is a great place for them to wait for the next host to be loaded on. You never know what the last animal that was in that trailer poopin, breathing, dripping snot, and peein might have had.
If you really think they are leaning toward pneumonia, it's time to call a vet ..yesterday. It works fast and can be very difficult to control and all the 'good stuff' medicine is by prescription anyway.
Don't wait on this..
As I told you via PM, what may be applicable here in E. Texas may not be the right course for North Carolina.