Set up Mac with the same iCloud

Look at this:

Set up iCloud on your Mac - Apple Support

It includs this:

Sign in to iCloud

1. 1. Choose Apple menu  > System Settings. 
   2. At the top of the sidebar, click Sign In with your Apple Account. 
   3. Enter your Apple Account email address and password. When you sign in, iCloud is turned on automatically.

If you're already signed in to iCloud, you see your name at the top of the side panel or at the top of the window.

So-- you just use the same account email and password, and you're in!