I have two Hampton Bay ceiling fans, model UO7078T. They are in different parts of the house (not close together) yet when one remote is used it operates both fans. Not a good thing when someone is trying to sleep and the light suddenly turns on.
Is there some way to put them on different frequencies?

Check the battery compartment of the remote. There should be a row of 4 little switches. Somewhere in the receiver, another 4 like them. Reset at least 1 switch in both the remote and the receiver. Leave the other remote and fan alone. Each remote will then only work the fan with the same switch settings.

Sometimes the canopy compartment can be quite packed when a remote unit is installed. Please make sure the power is off and stays off before opening the canopy up as wires could pop out and wire nuts can quite easily fall off. This is doubly true if the electricians were using the little nuts that come with the fan.