If there’s no similarity between the two, I’d say keep them separate for now. If they both build a large enough following, you can back into the content network umbrella eventually and say it manages both.
The scalability challenge is going to stem from the topics and niches primarily.
Those are pretty diverse niches to me?
My 2c, although not an answer to the question Is figure out how you’re going to make the production of the content scalable. Worry about the separate brands and whatnot later…. unless one is a clear leader with traction already.
Ideally all sources should leave to one. Podcasts works best when there are already good no of listeners followers on channel. Helps in building First impression of the channel. Creates buzz when two people discuss a podcast they heared. My vote Single Channel