To rule out any duplicate IP address issues, can you follow the steps in this article:

It sounds frustrating that your Play:3s are having trouble grouping with your other Sonos products. Here are a few troubleshooting steps you can try:

1. **Check Network Connection**: Ensure that all Sonos devices, including the Play:3s, are connected to the same Wi-Fi network. Sometimes, network issues can prevent devices from grouping.

2. **Update Sonos App**: Make sure your Sonos app is up to date. Sometimes, outdated software can cause connectivity issues.

3. **Reboot Your Network**: Restart your router to refresh the network. After rebooting, wait for a few minutes before reconnecting your Sonos devices.

4. **Group via the App**: Try grouping the Play:3s with other devices through the Sonos app. Go to the "Rooms" tab, select the room with the Play:3s, and attempt to group them with another room.

5. **Check for Interference**: Make sure there are no physical obstructions or electronic devices nearby that could interfere with the Wi-Fi signal.

6. **Sonos Support**: If none of the above work, consider reaching out to Sonos support. They can provide more tailored troubleshooting steps and identify if there's a specific issue with the Play:3s.

I had a similar issue with a Play 3.  I moved it to near my router and connected an Ethernet cable directly to it.  After a reset, powering off/on, etc. a few times, the system was then able to connect and do an update, then it finally started working.  I left it that way for the day, then disconnected the Ethernet and happy to say it still works.  

The rest of my systems are still a frustrating mess, but that fixed my Play 3 issue.  :)

 Don’t know if the Play 3 is at a firmware “dead-end”.  If not make sure the Play 3 firmware is the same version as the other speakers.  If not see if the Play 3s need an update.