How to set up a site mirror?

Question

Search Engine Optimization

There is a site 1. Last year we made a copy of it with a new domain: site 2, put a 301 redirect from site 1 to site 2. We moved the site in the webmaster panels to Google and Yandex.
After some time, the site was re-glued, site 2 became the main one and took over all the positions of site 1 in the search engine. Site 1 pages all left the search engine. Until today, the redirect from site 1 to site 2 is not disabled so that old clients do not lose us.
Site 2 has changed a bit in content over the year.
Now we want to change the domain of site 2. We made a copy with a new domain - site 3. And the question arose: do we think correctly - should 301 redirects be placed from site 2 to site 3? Site 1 doesn't need to be specified anymore, does it?