Is your intention to have all 4 of them have things programmed onto them, or are you just looking for the lights?
If it’s just for the lights, proximity isn’t really an issue, but if you’re wanting to actually use them, the interference can cause data corruption, and such. So you’d probably need to shield all of them except the one you’re trying to read/write to, any time you need to read/write. And, for readers, some of them might get confused by getting signals from multiple tags on the same freq.
It may be worth checking this post out, if you’re intending to use the tags for more than just lights.