If we are about 5 developers working on web/mobile applications on our laptops in our office, how can we use Git to do a team work?
Is it a good idea to use private repositories on Github or Bitbucket as we work on a commercial project and do not want to public our codes?
Is there a way to use Git locally in our company between our developer team? How?
You can use a self-hosted repository such as gitlab or gitea/gogs. Gitlab is pretty full-blown with commercial and community (free) versions, gitea (which is a fork of gogs) and gogs are very light-weight. I run gitea on my private server for stuff on which I'm working from different development machines. For just 5 developers, it's probably all you need.
Of course, every self-hosted option requires to set up a server that is reachable by all users. This can be either an on-premise server if your company network has static external IP addresses, if not, I'd rent a minimal virtual root server (this is what I have for private mail, web applications, and other stuff.)
I'm not aware of any Peer-to-peer git options, if they exist they are probably not viable between just 5 developers.
