Not a good idea to turn off the 5GHz band, mobile devices work much better using this.
To split the bands in the settings just give each SSID a different name, like myhome-2 and myhome-5 you can use any name whatsoever, but steer clear of most special characters. As to the passwords they can be the same or different, it’s up to you. Also it’s best to turn off smart/intelligent WiFi as this can cause some problems. If you ever have VM pods both bands must be active with one SSID and smart/intelligent WiFi turned on.