Extending Laptop display to two monitors
I think you might have answered your own question with your comment about the HDMI splitter! There may be a piece of hardware that will let your HDMI port be split over 2 monitors (so both monitors are half of one picture) but you would need to look that up. You might be able to get a USB video card or a dock, but that has its own issues.
If you need 2 extra screens, you have a Mini Display port as well. Just use that.