Hi Pati.
You asked "What are the chances that I have two broken keyboards?", well the chances are quite high really, especially since you also said that you require two keyboards plugged in to log-on because the defective keys are different on the two keyboards.
Ignoring the latest keyboards that come with fingerprint readers, a keyboard is basically a dumb device, it just sends a standard "coded" signal when each key is pressed and that code can be modified when more than one key is pressed at the same time, such as when holding down the shift key to produce a capital letter etc.
The code is send as binary string and so problems with low keyboard voltage can not change the content of the key-code, the key press will either be recognised and sent to the computer, or not.
There are a couple of very simple tests you can carry out.
Disconnect your old suspect keyboards and plug in any other keyboard that you can borrow, it doesn't even need to be a Mac keyboard, the key codes for the alphabetical QWERTY keys are identical for a Mac or a Windows computer keyboard.
If you try this does the borrowed keyboard work as expected?
The macOS includes a "virtual' keyboard, sadly not available at login, but useful for verifying keyboard and basic software recognition of the keyboard key-codes.
Open Mac System Preferences, click on Keyboard, then click on Input Sources and check the option "Show Input menu in menu bar" then close the Preferences window.
At the top of your Mac desktop the menu ribbon now has an oblong keyboard icon, click that icon to show the Input Sources menu and click "Show Keyboard Viewer".
A virtual representation of the standard Mac compact keyboard now opens on your desktop.
This virtual keyboard has two functions:
Firstly, as you press the real keys on your real keyboard the outline of the corresponding key on the virtual keyboard changes colour, the outline of an active, pressed key changes to a dull red, use the real shift key on your real keyboard and the displayed letters in the virtual keyboard change from lower case to upper case.
You can use the virtual keyboard in this way to verify that each of the real keys on your real keyboard is sending the correct key-codes to your Mac when you press them.
The second function of the virtual keyboard allows you test the macOS is correctly translating the key codes into valid characters as you type into a document.
Open the Notes app and select File > New Note, click anywhere in the New Note window to place the cursor and type into the note by clicking the letter keys in the Virtual Keyboard using mouse clicks only, do not use the real keyboard at all.
You can now verify that your macOS is correctly interpreting the standard key-codes and entering those letters correctly into your Notes document.
Armed with these simple tests you can verify that your real keyboard(s) are working, or not, and that the macOS correctly translates standard key-codes into the correct characters.
I suspect that using the tools described above will show that your two keyboards both have defective, worn-out keys.
Working on a busy university campus with several hundred staff our IT department replaces ten to twenty keyboards every month, luckily we only use inexpensive wired keyboards here and not expensive wireless, otherwise our IT costs would be enormous!
HTH
Will.
