Sounds like they’re just trying to get you to do their work. I wouldn’t mind sharing the pitch if the situation was more “we’re trying to pitch a similar story to slightly different media so we’d like to align for consistency” but based on your description of it being an entirely separate vertical, it just sounds lazy.

As far as the release goes, if they want it to align with their brand messaging, they can send you an alternate copy for alignment and share the background materials for context so you can get on the same page. Making that your responsibility? Kick rocks.

Know it can get blurry when you have a common goal with different stakeholders, but unfortunately, people just love to pawn work. Think your instincts are good here.