You’re not the only one with this problem: Post Processing with multiple cameras is currently very problematic
The best way to fix it is if you have an enterprise support contract, go yell at Unity devs and tell them to prioritize fixing it. But for us plebs, we have to resort to various hacks. In your case you might be able to render both cameras to RTs without using stacking and without any PP, composite them yourself, then apply PP to the final result. I’m not sure how much performance that would cost; it probably would be reasonable on PC/console but pretty massive on tile renderers like mobile.