I want a second Mendix app that creates records for an existing Mendix app. The problem is, that in App1, there exists and Entity1 that relates to Entity2. App2 needs to create Entity1 entities, but without the association to Entity2. The issue here is, that App2 will destroy the schema of App1. How do I integrate 2 Mendix apps on the same database?
You can't run two Mendix applications on the same database. In the way you're describing here, it would lead to tons of issues too in terms of data integrity. I recommend using webservices to achieve what you want here.