You'll want to use Sennheiser Wireless Systems Manager (WSM) with your G4 units to do the scan and coordination.

You will need to make sure all the receivers are networked to your computer using a network switch (100 mbit is fine) and then WSM can use one of your receivers as a scanner.

The scanner is called "Spectrum Analyser" and it's under the "Applications" menu at the top, near the Help menu.

In the top left of the Spectrum Analyser you can select which receiver you want to use as the scanner, then hit the red record button to do a scan. You then save that scan, load the Frequency Manager from the top menu and choose "Professional Setup". From there you can load in your scan and get WSM to calculate the best frequencies for you to use, and automatically send them to your receivers.

The last step is to re-sync each belt pack to its relevant receiver.

You can set the various beltpack settings through WSM as well, and when you sync the pack it will load all the settings from the receiver.

The process is actually quite involved, so you should look at getting someone in to show you how, and video the process. Or maybe you can find some tutorials o Youtube or something.