There was an even a (quite crappy) Amiga game! Coincided with re-runs on Turkish (newly formed) cable TV - such good (or not) memories.
https://archive.org/details/zx_Thunderbirds_1985_Firebird_So...
Edit : to set up controls since it's not noted on that page, you'll need to press R ( Redefine keys! ) and that'll get you started!
How to play : you swap between thunderbird 1 and 2 each ship by pressing spacebar ( default ) or whatever you configured it to. You'll notice the ship selected in the bottom left corner of the screen.