What to do about co-founders?

I would be honest with them, and present the facts.

Honesty should be the base for your management, if your right and left arms are not on the same page as you, then your company will suffer.

If you identified the project manager to be amazing for business then tell him that you want him to solely focus on business and leave the part of strategy for the 2nd co founder.

If you need cashflow for the second person and you don't have it, maybe you need to make a cut in both your and the 1st cofounder cash to bring in the 2nd person.

At the end of the day seems both of them are important and if they are in the same page as you both of them will understand your choices or maybe suggest even a new approach you have not thought about.

Option B would be you ponder which of these 2 people would have a bigger impact on the company success and you take the role of the one you would need to let go. But personally I think letting go someone would be harder than trying to discuss a share of pain for future success. Specially if both of them are important for the success.