Search for "RE5 4 Player Mod" on Nexus Mods or the Resident Evil Modding Board . Look for version 2.1.0 or newer. You’ll get a .rar containing:
To achieve 4-player co-op, players typically rely on the Gold Edition of the game and specific community-made trainers or DLL hooks. The most popular method involves using a combination of the Raz0r & Geri Trainer and the Maluc fix. These tools allow the host to bypass the hardcoded two-player limit by tricking the game into accepting additional connections. Because the game’s story mode was never intended to house four protagonists simultaneously, the mod usually functions by spawning extra characters—such as Jill Valentine or Josh Stone—who then take the place of AI entities or occupy hidden "slots" in the game session. Resident Evil 5 4 Player Mod