Syncing 2 Arduinos with 2 433mhz RFM69

Trying to make 2 race timing trees, where one activates the other. I've got 2 UNOs that already have the same sketch on them and they function off the same momentary switch. I'd like one to activate both, the second one wirelessly. OR if it's just as simple make them both capable of activating the other. I have absolutely no idea where to begin with these things. It would be best if there was a way to sync both. Looking for ideas and direction here.