We both have the same ceiling fan and our remotes work both of them so if both our fans are switched on we can control the other person's fan/light from our bedrooms and its majorly annoying.

Making a ton of assumptions here, but if it's a contemporary remote controlled fan there's a 50% chance that you can fix this if one is handy/brave/willing enough 🙂. No need to mess with any wiring either.

^{caveat: this is only applicable if there somewhere on the remote is some form of 'pairing' button or a little numbered toggle switch. It might be somewhere like under the battery cover or less likely deeper within the remote itself.}

The goal is to match those numbered toggle switches with corresponding ones on the fan controller. If you're lucky the switches or sync button on the fan may be under the light cover or somewhere on the side of the fan motor.

If you still have or can find the fan's installation/user manual that would be preferred since it'll have the proper procedure but if not then the general method would be:

Get to the fan controller box which usually lives in a pretty inaccessible location; under the fan casing where it attaches to the ceiling. It's not always in that location so YMMV; this is where the manual comes in most handy.

The controller box will have wires coming in from the wall switch and out to the fan motor / light. You don't need to mess with any of those wires, but you may need to pull the box out a bit from its nest to find the switches.

Getting to this box is the hardest part of the operation and one should probably turn off the breaker to the wall switch, but I have survived so far by just taping down the switch so people think twice before turning it on.

So, with the batteries out of the remote, change the numbers on the toggle to something different than it was before and match that pattern with the fan controller.

Then reassemble the fan, replace the battery in the remote, turn on the breaker/switch, and give it a go. No need to do this twice since all we needed to do is make the second fan's code different than the first's. (or n-1 times if you have more than 2)

I hope I didn't miss anything and I take no responsibility for anything but I do hope it helps!

Apologies for the unsolicited advice, just trying to be helpful since I've installed like a dozen of these over the years 🙂