I got my brother to sit down and look through this with me. He says he doesn't want to replace anything, except inside the JJ2 folder, in which case it won't influence the rest of the PC. So we placed the correct msctf.dll in the JJ2 folder, but it had no effect (logical, there aren't any other dll files either so JJ2 reads them from somewhere else).

Nothing more can be done. Thanks for all the input anyways.