What I try to achieve is to have the portfolio slug as a page slug also, and when I will assign the page as a parent to another, then that page must look for a specific page’s parent ID and return the correct results.

If I have the same slug in portfolio and in a page and try to create a child page, then I will get an error.

Example: Portfolio slug: test/rent-a-car. Page slug: test/rent-a-car.
If I create a page test/rent-a-car/child-page, then the child page will give a 404 error.

Is this possible to be achieved anyhow?