Fear Platinum base game works fine after applying the fix for it and i'm going to play that first (but have completed it before) but how the heck do you start the two expansions? All I get when I press New Game is the option to choose difficulty for the base game.
I have played all three....when installing Fear Platinum, the GOG installer installed all three games on my PC. (I don't use galaxy, but download directly, so if you used galaxy, I can't help there). It also installed three separate shortcuts on my desktop to access the 3 different expansions/games. If you didn't have this happen, then I can only suggest looking in the games folder on your hard drive and see if the shortcut exes' are there, and then copy them to your desktop if desired. If not there, then save any relevant data/saves, un-install, and re-download and reinstall the game. All three games should install with the single GOG installer. If that doesn't work, you'll need to contact support. Good Luck