You would really need to describe your network setup in a little more detail, before suggestions can be made. Here are some things that might help the community here to understand your issues.

• Make/model of router?
• Other WiFi access points?
• Wifi channels in use/Channel-width?
• If using SonosNet and how many devices wired and where to (distance of wired device from nearest AP)?
• If using SonosNet - if you have chosen to retain the WiFi credentials on your devices?
• Details of primary Sonos controller device - iOS/Android etc. Version of operating system?
• Anything else you think might be relevant/helpful, like ‘managed’ switch settings etc?

It would also be helpful to know what troubleshooting steps you have taken so far?

Try hardwiring one sonos player using ethernet cable, this will solve your problem

What is the history here?  Did these work previously on your system?  If so, when did they stop working?

Or have you just bought them second-hand?  If so, did you factory reset them before trying to add?

Wiring each speaker as you add it sometimes helps.