Hi moushkka,
There are a few options that you can use to make a custom Engine version available to your team. The first option is to include the engine source code in your project repo. This may be the simplest option, but it would result in everyone on the team having to build the Engine themselves. It would also significantly increase the size of your repo.
Another option would be to create a separate repo for your Engine source code. This would keep your project and Engine code in different repos, but would still require everyone on the team to build the Engine themselves.
A third option would be to create what is referred to as a Rocket build of your Engine. This is a pre-compiled binary version of the Engine that you can distribute to your team. There is some additional setup required initially, but once it has been built it can be distributed in binary form to other team members so they do not have to build the Engine. It is not something that we support directly at this time, and there is very little documentation for how to do this, but it is something we hope to simplify and expand support for in the future. This forum thread may be helpful if you want to try this option.