How to properly organize git repositories in this case?

Question

git

Situation: there are 4 independent sites, the engine is exactly the same for all, the sites differ only in templates and content. There is a lot of work on these sites - finalizing the functionality and layout. The code of the engine and views is delimited and lies in different directories.
Task: organize the repositories in such a way that when the engine changes on one of the sites, the changes are automatically distributed to the remaining 3 sites, and the template changes are applied only to one. the trick is to keep the engines identical by not doing the same job 4 times.
so far I see one repository with four branches for each site, each of which is divided into frontend and backend branches + a common branch for the core. and then carefully merge everything. but with a probability of about 146%, sooner or later I will mess up and get tired of raking all this.
is it possible to create a separate repository for the common part and automatically merge it? is it possible to merge individual repositories at all?
who faced a similar problem - a help.

Answer 1

Make one repository for backend and 4 repositories for view?
The structure of the projects as a whole will be as follows:

MyProjects
............/backend
............/frontend
......................../one
......................../two
......................../three
......................../four

I would do so, although there may be more beautiful / correct options.
Хотя можно вообще так:

MySites
......................../backend
......................../one
......................../two
......................../three
......................../four

И для каждого свой репозиторий.

Answer 2

What requires separate versioning is placed in a separate repository. Branches are used to distinguish between different versions of a particular project, but not as between different projects.