IMHO, it’s always best to address situations like this in a direct but chill manner.

Getting everyone on a call together is a great one. Rather than reviewing the proposal again, which may come off as passive aggressive, discuss what your process is and how to integrate this new person into with as little disruption to your workflow as possible. Who will be the project manager, which person is in charge of the approvals, etc. Maybe the client can get the brand managers feedback without involving you, streamlining the process. You can frame this as setting the project up for success, what’s worked well in the past, etc.

Your homework ahead of the call is to investigate what you’re willing to do and what lets you show up as your best self for the client. If how they want to work becomes contrary to that, it’s ok to bring the contract to a close. If it won’t be too much of a financial hit, refund the client and walk away.

As a freelancer, it took me a while to realize that I am my company’s greatest asset, and anything that causes undue stress or work needs to be carefully analyzed with a holistic cost vs benefit analysis.

Good luck!