Looking for advice on adding a router to an existing network to make 4 devices accessible remotely

Hi,

I have a small office with an existing network. We're about add 4 employees that will be working with a remote office. I'm looking to have their 4 computers as well as any other device they use to go through a separate router (I bought Linksys AC1200 for that) that can be accessed from the head office overseas without affecting the rest of the office. How do I go about setting that up?