I will be new to beta. When there’s a beta firmware update, can I install it on only one or two of my 12 cameras? (I don’t want to install in the more important locations). How will I know which firmware is beta?
Beta firmware will be discussed here and in the Core Users group. You can choose which cameras to install it on pretty easily by declining the prompts and manually upgrading the firmware in your Camera Settings.
Welcome to the beta program! 
Upgrade is done per camera. You can be selective on upgrading your firmware, 1 or 12, all your choice.
After updating cameras to the Beta Software, should I hard reset the cameras?
I did not. I just installed the beta app, and from there installed the beta firmware. There are a few possible known issues:
If your WyzeCam does not auto reconnect back to the network after the firmware upgrade, please unplug it from the power source and then plug it back in; it should reconnect back to your network. If night vision seems to be not working after the firmware upgrade, please use your Wyze app to turn night vision on and off once; it should start working again.
Can’t wait to help make Wyze better!