I guess you used some kind of software that was supposed to be able to open/convert these textures, but it seems like the textures in question were in a different format than expected by the tool. I recall PS1 game resources often using the same file extension for different formats of the same kind.
Either you try to find another converter. Or you try to find some kind of tool that can display/dump video memory within an emulator.
The latter option, using an emulator and dumping the textures, has worked well for me in the past (for the destruction derby mod), so I would try that first
Seems like they have an alpha channel (for transparency) to me? Something like that or the tool you're using doesn't properly support their format. Or both.