File synchronization between 3 places?

An unorthodox idea, couldn't you just use GIT?

Does the data change at all places all the time? Otherwise you could start your work by doing a rsync from one (that you declare as the master) to the machine you work and then rsync back when you are done.

I know I'm late to the party, but it is possible to synchronize 3 (or more hosts) with unison. I do this regularly with four machines. I created a star-shaped topology, in which one host is designated 'central', and the others synchronize against this 'central' node, never against each other. It is easiest if there are no changes on the central node. In your case, this would require a fourth node.