(By the way, I've never seen the spelling "GeTTY". I don't think it's correct.)
The short answer is that you can disable
getty by commenting it out in
/etc/inittab and running
init q to reread configuration. Unless you're using systemd or Upstart but since you didn't say so I'll assume you aren't.
The longer answer is that your setup has an intrinsic problem and is flawed. With
getty running on both serial ports, the two
getty processes run the risk of starting to endlessly chat with each other. That is, one will send a prompt, which the other one interprets as a username, which causes it to produce its own prompt, which gets interpreted as a username on the original end, and so on forever.
The correct way to handle this is to use two serial ports, one in each direction. The console serial port on system 1 is connected to the extra serial port on system 2, and the console serial port on system 2 is connected to the extra serial port on system 1. Since the "extra" serial ports on both systems never run
getty (only the console serial ports do), there is never a
getty to disable, and the port can be directly used by
For the "extra" serial ports, you can use USB serial port adaptors if the systems do not provide enough built-in serial ports. Because those ports are only accessed after the system is fully booted (unlike the console serial port) it's OK for them to be on a USB bus which will not be initialized until partway through the boot sequence.