There isn't a simple way to do this, unless they all use the same data model.
If that is the case then you can just:
1. Duplicate the biggest app (to act as a base)
2. Copy and paste the sheets from the other two apps into the main app
3. Rearrange and edit the sheets so that the new app is coherent and provides a good user experience
You will lose all the bookmarks and user sheets from the other 2 apps.
If they do not share the same data model then you first are going to need to do the work to unify that before you can combine the apps.
