If your two local machines are windows based, then look into remote desktop, which is a native windows feature.
For connecting to your brother-in-law where both are running Windows, then AeroAdmin might be an alternative to TeamViewer.
There are some limitations on the free version, like max. 17 hours per months. The rest of the limitations should not apply if it is just you and your brother-in-law.
https://www.aeroadmin.com/en/index.html