Growing co-founders?

I founded a (very, very small) startup a couple of months ago with a friend and a brother-in-law. The friend is our front-end developer, the BIL is our data analysis guy. I'm the back-end dev, but also the guy learning the business, sales, and management side of everything.

I keep wondering whether and how to start my co-founders on the business side of things. I'll talk strategy and business needs with them, but the question is whether I should be working to train them in strategy/management/everything else too, or should I let them focus on their core areas?

I worry: 1) they will begin to feel more like employees than co-founders if I'm running all the business aspects of our business, 2) they won't be able to give me good advice because they won't know if I'm being an idiot, and 3) if our company actually grows beyond 3 people, they won't have the context and skills to work as well managing as they do as contributors.

I've read a lot on co-founder management, but I don't know how to address this or even if it's an issue. Any thoughts?