If you are trying to use Wavlink as an extender, verify that it is in Repeater or Relay mode. (Settings in Wavlink should mirror those of old router re: gateway IP, wireless channels, modes/protocols, and wireless security) If you are using it in Router or Access Point Mode and your other router is still connected to network, the Gateway IP address (192.168.1.0 or the like) has to be different than the old router. I am unclear as to whether you have swapped routers or trying to extend coverage.
Basically, verify that you do not have 2 routers set to Router Mode that are using same gateway IP address. (The 2 router's DHCP servers will conflict with each other trying to assign IP addresses to wireless devices).
If you unplug your old router from power and use your Wavlink set to Router Mode, can you now connect to your Roku devices?
Since your Roku devices are seeing the new router, it's using an accepted channel. You are saying it's not accepting your password, so check your security settings in the new router. Make sure you're using WPA2 as the security level. Also make sure your password isn't using special characters (like @, #, $, etc.) as some Rokus don't like using them. Just stick with upper and lower case letters and numbers.