To sync two Google Drive accounts to your Windows PC:

  1. On the web interface of Google Drive, access your Google Drive #1. Share the contents of Google Drive #1 with the user of the Google Drive #2.
  2. Access the contents of Google Drive #2. You will find Google Drive #1 contents under “Shared with me”. In the drop-down menu that shows when clicking on the three vertical dots, choose “Add to My Drive” to move the content of Drive #2 to your the main content area of your Drive #1.
  3. Sync the contents of Google Drive #2 to your Windows PC.

Source: https://support.google.com/drive/forum/AAAAOxCWsToVIrTVRJPsSI/?hl=en