@AMCross 

Good day.

Sorry for the delay.

RE305 V3 itself supported OneMesh but it needs to work with TP-Link OneMesh routers.

And normally, we would not suggest to set up the extender one by one. If no other choice, please make sure the extenders are no more than 2.

So if possible, you could relocate the virgin media router in the center and put all RE305s around the router and connect all of them directly to the router;

If not, please try to set up different SSID to see if the devices could automatically choose the strongest signal;

And if you just bought RE305 and within the return period, it would be much better that you could replace RE305s with the Deco mesh system:

https://www.tp-link.com/home-networking/deco/

Thank you very much!