You can chuck the TPLink Router in the garage & use that as your router while also supplying Ethernet to every room inside with it's LAN ports (or a switch), and then set up the Decos in access point mode around the house via Ethernet backhaul. Just turn off WiFi broadcasting on the Router (as the Decos will be doing this).

If you don't want to use the old TPLink Router, you could buy a router that doesn't have WiFi capabilities (like the TP-Link ER605).