This is a wonderful teaching oppotunity, take heed to the necessity for QUARANTINING incoming animals to your farm. If you fail to quarantine you are asking for trouble.
I hope you can rebuild your flock and keep them healthy.
I truly hate this. I guess you know your options and it is going to have to be up to you to decide what needs to be done. Just remember that we are all here for your moral support if you need a shoulder to cry on, so to speak.
So sorry to hear about the diagnosis. It is going to be so hard for you to do what you are planning but that is the only way to remove it. Don't you have to sterilize everything in the coop also? UGH!!!