Answer 1, authority 100%
Use the File / New View into File menu. A copy of the file will be created in one of the windows, which can be dragged into the other window.
Open two different files in your
Sublime , drag one tab to the desktop, it will pop out into a separate window. Then drag the file you need into the first, and then into the second window, close unnecessary tabs, and you will have one file open in two windows.