Since this is a combination services and OS question I am posting it here..

I am looking for a way to sync laptop user files with the same accounts created on the mac mini server and to setup sharing too..

I guess what i am looking for is your own home supplemental iCloud to sync what apple iCloud service does not sync.. plus you provide the storage so it doesn't cost anything.

Are there any add on apps for apple server that would do this on a mac mini?

The ultimate goal would be to login to the server and see all of the files that are on your local laptop under the users account.