I posted another question earlier about trying to export my object keeping all the textures and materials intact and I was told the issue was that I haven't merged the meshes into one and UV unwrapped the result. I did attempt to do that but that process broke all my textures and I couldn't get them to go back to the way I had them before. I addition, the UV map became very messy and the seams didn't work the way they did before. I managed to get everything fairly straight and flat again, although some wouldn't straighten out at all, and also managed to get it so none of the islands were overlapping. But even after "fixing" the UV map, I still could not get the textures to go back on properly.
I was also told that I needed to bake the textures before merging them and apply those textures after the merge but now the issue I'm having is that the texture won't bake properly. It puts these weird lines over my texture and the texture image I'm trying to bake to is still just solid black. I'm not sure what I'm doing wrong here as I'm only very new to Blender.
I'll also provide a link to my .blend files and textures, there are three .blends, one after baking, and one for before and after decimating the meshes as I'm not sure if decimating it is causing texture or UV issues or not, so I've provided both versions. Link here: https://drive.google.com/drive/folders/1lJp7Q-mkAsGS8jgc3275Bb4qrNzEgJMF?usp=sharing