I am not familiar with that app or how it works as regards to individuals. In general, though, each person should have their own Apple account. If this is an app that costs money you can use Family Sharing.
Make sure that each family member has a unique Apple ID --> Make sure that each family member has a unique Apple Account - Apple Support
- "If you want to share purchases or subscriptions with family, use Family Sharing. Each person should use their own Apple ID."
This article explains how to create a new Apple Account --> How to create a new Apple Account - Apple Support
To learn how to set up Family Sharing, read this support article --> How to set up Family Sharing on your iPhone, iPad, or Mac - Apple Support