First, don’t let it try to update the 3 working cameras until you determine what caused the first two to fail.
What version was it offering you? I’m in the beta and my v2 cameras are running 18.104.22.168 firmware. And I have Android App version 1.5.42 (now public as well). And they updated without issue. I am not sure what version they upgraded from.
First thing I would try is to make sure you have the latest version of the App loaded. The firmware and app need to be using the same features.
There is a manual firmware upgrade method that involves downloading a file on your pc, copying to a microSD card and holding buttons. I have never had to do that yet, but others reported success. Some of the commenters said they had to double press and hold to get it to work, not sure it this is just coincidence or a fact (I find it hard to understand how double pressing when the camera was powered off could affect anything).
If you have a microSD card you can use, and you want to try reflashing, here is the thread https://www.wyzecam.com/forums/topic/flashing-your-wyzecam-v2-firmware/
It doesn’t have the version I am running, the latest version in that thread is 22.214.171.124-1, but since 126.96.36.199 was “released to the public” on Sept 17, I am not sure why it isn’t in the above tread. Perhaps there have been issues and it was pulled, or perhaps they never updated the post with a link to the new version. That seems unlikely, I don’t see a lot of complaints in the https://www.wyzecam.com/forums/topic/v2-firmware-4-9-2-42-released-to-the-public/ thread.