Migrate multiple journals into one

We are about to migrate four OJS journals with versions 3.1.2 and 3.2.0.
The idea is to create a magazine portal so that it will then be redirected to a specific magazine.
In case of unifying the database, is there a tool available to carry out the migration?
And in the case of the main web page of each magazine, how would it be to move the files and the template?
Users should only have access to a specific magazine.

I think there is no automatic way to merge different instances into one.
Probably export/import of submissions is the only option (with all the data loss that implies).

Import/export is one of the big items on PKP’s roadmap, but it will be a long road:

Why not keep them split and build the magazine journal in the front of them with a different tool?

This is a 10 years old drupal (I mean, look&feel need to be updated) but the idea is still valid: