How to clone many projects from a single fork and have them all auto-update and able to send merge request?

I have a Gitlab account, I’m using and committing an open source project that has a repo in Gitlab.
I have a fork of the project, it is auto updated regularly and I can create merge request.
I usually work in and with a specific branch (not master).

What I need now is to create several children projects that should be also getting their code updated from the main project repo/branch (or eventually from my fork/branch).

On those projects some commit should stay locals (not being committed back anywhere).
Other commits (fix) should be pushed back to my fork from where I will create merge request to the main project repo.

I tried a few things but couldn’t get it right and simple.
Anyone with knowledge and experience can help me ?