I was thinking a laser rather than radio. In radio terms: very very high gain. The receiver can be a mylar reflecting dish, which would be lightweight. Use a

I was thinking a laser rather than radio. In radio terms: very very high gain. The receiver can be a mylar reflecting dish, which would be lightweight. Use a gyroscope to steer the entire probe (both for transmitting and receiving). They only need to communicate very very sporadically, and you only need a single bit of data transmitted (amongst each other). Make some kind of schedule where the probes face each other, measure distance (i.e. time between send and reply), then steer toward the next probe. To earth you would basically use Hubble to read the data (and let each probe send duplicate data back to earth).