C2 supports WDS bridging, but it may or may not work with VR900. https://www.tp-link.com/en/faq-1385.html Beside range extender, there is powerline extender

Is your internet IP address static and public? If it's not public, you need to open port for the router from the uplink device or from the ISP side if you are using sim card. If it's not static, then...

Yes it will work. Use M9 plus as main deco. https://www.tp-link.com/en/faq-2248.html

Reset it, try again. You can contact tplink tec support to get some advice.

Beside away mode, no other schedule settings? How about reset one of them? Contact tplink tec support to ask for solution

Thanks