For anyone who finds this thread, here is how I solved the same problem:
The easy bit:
1. Split the 2.4/5ghz signal - see thread here - https://community.plus.net/t5/My-Router/Having-to-switch-between-2-4GHz-and-5GHz/td-p/1709284.
The tricky bit:
I kept getting failed to connect. Eventually, the Ring app would say something like "you previously tried to connect to X wifi, do you want to try again?". Even if this is what you want, you need to click no, then you get a list of wifi networks. Select yours and you should be prompted to enter the password. There was no problem after that.
The issue seems to be that without doing it this way, Ring was not giving me the opportunity to provide the wifi password, so the connection was never going to succeed.
