To everyone who's having issues with the monitors having missing textures even after mounting half life and both of the episodes:

The fix I found that works for me and my friend is downloading the source mod from moddb (https://www.moddb.com/mods/breadmans-ghosthunt-mod, its an all-in-one download for all 3 maps) and putting the folder that extracts with the readme file into the addons folder of garry's mod (steamapps\common\Garrysmod\garrysmod\addons\).

The game recognizes it as an external addon and finds all 3 maps AND fixes the remaining missing texures.

This is mainly here for those who are hellbent on playing this in gmod and dont want to add it as a source mod into steam or want to play with friends (the source mod version doesnt support multiplayer afaik).

Hopefully this saved someone some trouble.