How can I use 2 USB Headsets on one Macbook?
You don't need special hardware for this. Plug in both headphones, then open Audio Midi setup from /Applications/Utilities. Click the plus in the lower left corner and choose "Create Multi-Output Device." Check the checkboxes beside both headphones in the new panel on the right. If you want to rename it, you can double click the new entry in the list on the left and give it a name like "Both headphones."

Now you can choose the Multi-Output Device as the audio output in System Preferences → Sound. (You can also easily change the output by holding the Option key and clicking the volume menu.)