It looks like they have taken a reaction to the vaccine, Twisted neck(star gazing) is a sign of the brain being infected and overheating it could be any number of things including paramyxo or pigeon menangitis, best to get the vet to do a live post mortem and find out the true cause it may be that you will lose a few if not all your birds but I would cull any showing signs of twisted neck Here is a good sight for general knowledge on pigeo ailments http://www.pigeonrescue.co.uk/injuries.htm