Is it considered splitting up if two of our team members hunt on one end of a ranch, and the other two hunt the other end?

Yes. That is the definition of splitting up. All team members MUST hunt together. A good rule of thumb is if you are hunting off of the same caller, it is not splitting up. For instance, while hunting during the day, you set the caller out on the ground, and your team spreads out to hunt animals coming to that call — This would be within the rules.