What are some lightweight two-pane GUI file managers that support network features?

Double Commander is another option! You might need to tweak the settings a bit to get it looking just right, but it works well.

Midnight Commander (mc) is a great choice! It’s primarily a command-line tool, but it does support FTP too if you need network access.

Don't forget about TUI file managers like Ranger and mc. They can be super efficient once you get used to them, especially for SSH work.

If you're looking for something more modern, both Dolphin and Gnome Files (Nautilus) have split view options. They’re quite user-friendly!

Have you tried Thunar? It offers a split view feature if you press F3, which makes it easy to navigate between folders.