Are you saying that you want to buy out existing apps that may not be positioned well?
I am an app developer, but recently to get an app built (React-Native), I found it easier to break down the requirements into a technical architecture so it was clear what the specific components are. I then hired two separate developers to do the scaffolding work and got about 80% of the way within two days. It was also defined pretty generically so that I could combine the discrete features on my own and protect the IP.
Hope that helps.