Is it like a QTE where you have to press Q or E at the moment the button prompts appear to change weapon for either character? I wasn't quite sure if you could pick up weapons from the corpses of enemies or if it was just a bug so it seemed a bit confusing to me. There is one bug I came across where if you die and press retry, the game freezes upon reloading the level and you have to press pause and then resume to unfreeze the screen and keep playing. Hope that helps!