magic keyboard typing 2 adjacent letters at same time

First use the keyboard on a other Mac to see if it's a hardware/keyboard issue. Or use another keyboard with your Mac.

If not a hardware issue Reset NVRAM or PRAM on your Mac - Apple Support a couple of times in succession.

If that doesn't help boot into Safe Mode according to Start up your Mac in safe mode - Apple Support and test to see if the problem persists. Reboot normally and test again.

NOTE: Safe Mode boot can take up to nearly twice as long as a normal boot as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

The following will require any USB keyboard and mouse. If you don’t have them, borrow or buy them, they are

inexpensive!

• Connect the USB keyboard and mouse to the computer.
• Open System Preferences – Bluetooth
• Un-pair the wireless keyboard and mouse.
• Turn off Bluetooth
• Restart the computer in Safe Mode per the directions in https://support.apple.com/en-us/HT201262
• Restart the computer normally.
• Open System Preferences – Bluetooth
• Turn on Bluetooth
• Re-Pair the wireless keyboard and mouse.
• Unplug the USB keyboard and mouse and begin testing the wireless devices again.

If you decide you want to get another keyboard, I would recommend using www.macsales.com, they specialize in Macs and everything they sell just works!

Keyboards have never been an Apple repairable component, as you have found out they should be replaced when they cease working correctly. As stated if you want to replace your keyboard, I'd recommend www.macsales.com, they have a wide variety of options so you can find one that best suits your needs.

Good luck.