One of ours has mycoplasma, she has had two bouts of it, the last time was ages ago. No idea how she got it though :roll: . My understanding is that it can be bought on by stress. My vet gave us extra treatment (I forget what it is now, looks like a bran type powder substance) for if she shows symptoms again, and touch wood, she's been fine. The other 2 got treated while she was being treated as they all eat from the same feeder. Since she first showed symptoms we have added another 6 chooks to the flock and they all seem to be ok, this we checked would be ok with the vet.
When were your dads chooks diagnosed? If I remember correctly it takes a couple of days to take effect. I hope they get better..might be worth double checking the dosage advised??