Obviously Awesome - April Dunford.
https://www.amazon.com/Obviously-Awesome-Product-Positioning-Customers/dp/1999023005
This is a life-changing book, not just about positioning - but strategy, marketing, etc. It all starts with positioning.
That's a great question. I'm going through a similar thought process for our product thoughtflow.io . Don't have a definite answer, but a few factors you might want to consider.
First principles
It's easier to scale something that solves a similar problem for a similar market because of the network effects.
Your messaging will be crystal clear lead to higher conversions when you have a specific target persona.
Factors to consider - Are the individual markets big enough
Are these adjacent markets?
Does use of your product in one market create visibility in the other?
In any case, whether you choose to go with single app or multiple apps, it would be better to launch and scale in one market before targeting another one. The easiest way to fail in the initial stages is to spread yourself thin.
Additional reading, that might help -