No keyboard in recovery mode on MacBook Pro so unable to mount encrypted drive
As a first step I would try resetting your NVRAM to see if that allows you to enter your password. It's unclear whether you'll be able to do this, since you need your keyboard to do so - but we actually don't know if the keyboard is the issue. In fact, since the USB keyboard didn't work, I suspect it's something else.

Reset NVRAM

Follow these steps:


Shut down your machine. Yes, a full shut down, not just logging out.
Press the power button and then press the commandoptionPR keys. You have to make sure you press these keys before the gray screen appears or it won’t work.
Hold those keys down until your Mac reboots again and you here the startup chime.
Let go of the keys and let your Mac reboot normally.


Note: When you log back in you may need to readjust some of your system preferences (e.g. speaker volume, screen resolution, startup disk selection, time zone information, etc).

If you don't hear your Mac reboot and play the startup chime again, then try the above steps from scratch, but try using the USB keyboard instead.

Let me know how you go.

Use Terminal in Recovery Mode to unlock your encrypted drive

Okay, since resetting the NVRAM didn't change things I suspect that this may not be a keyboard issue, but something else related to entering the password. So let's test this theory by trying to unlock your volume via Terminal. 

Follow these steps:


Boot your Mac into Recovery Mode
Launch Terminal (Utilities > Terminal)
Enter the filling command in Terminal: diskutil list
Now, because you have an encrypted volume you should see something like this:

Logical Volume DriveName on disk2s2
123E4567-E89B-12D3-A456-426655440000
Locked Encrypted

Now, to interpret the above example: DriveName will be the name of your drive, and the next line (i.e. the 123E4567-E89B-12D3-A456-426655440000 in my example) will be what is known as the universally unique identifier (UUID). This identifier will be a string of alphanumeric characters in a 8-4-4-4-12 format. The UUID is what you will need to unlock your encrypted drive.
Enter the following command in Terminal: diskutil coreStorage unlockVolume &lt;uuid&gt;

NOTE: Replace the &lt;uuid&gt; with the actual UUID for your drive.
You should now be prompted for your password
Enter the password (don't worry if you don't see the cursor move)
Press enter


NOTE: If you can't enter any commands in Terminal then we know the problem lies with your keyboard input. Either way, let me know how you go.