This might be a silly question... but have you tried the easy way getting private keys off your addresses?
if your bitcoin in your old pre-HD wallet addresses, their private keys are easy to extract
below is an excerpt from my post helping someone else, disregard some unrelated info 
if the menu is available you can extract private key for that specific address, it starts with K or L
if this works I can give you more information or probably you already know what to do next

Which version did you use? Try using the classic: https://multibit.org/release-info/classic/v0.5.17.html

And did you try this conversion tool: https://bitcointalk.org/index.php?topic=610555.0

You can run it on windows. Go to the link I mentioned above --> Clone or download --> Download Zip --> Extract --> Tap the HTML file.

*Run it offline for security

Download this and run it offline: https://github.com/blockchain/my-wallet-backup-decryption-tool
If your private keys showed up, You can now import it to whatever wallet you like e.g. Electrum

You can import via seed on electrum, Please refer to this thread: https://bitcoinelectrum.com/restoring-your-standard-wallet-from-seed/
Just don't forget to tap Options --> BIP39 Seed when electrum prompts you to enter your seed. Just to clarify you have a 12-word seed in you right?

https://electrum.org/#download *Download the latest version