I installed a new ceiling fan, it came with a remote.

Installed a second in another room, and bought an add on remote control.

In still another room, I added an add on remote control to an existing fan.

All worked great for a week.

Suddenly, none of the remote controls work, and the first fan light is dimming, then brightening, and dimming and brightening endlessly. All 3 are using different remote codes, and none of them even have batteries in them any more!

Any suggestions? Is my house haunted or is the wiring in my house doomed?

Static

Sounds like a loose ground. Be sure all your connections are tight.

Try changing the codes on each fan and remote, make sure each fan still matches it's remote.

Did you have a lighting storm or anything?

Ceiling fan remote controls - help and FAQ- Ceiling Fans N More