I don't think we have tried installing an
FM Trap. They are fairly inexpensive and usually available at local Radio Shack stores, (returnable). The symptoms point toward a possible interference problem.
If I were building from scratch, I would use a modest sized 7-69 combo such as the HBU-22, HBU-33 or HD7694P. All of those antennas should have no trouble powering many more sets than you have at the moment. If we are fighting multipath, the larger Winegard antenna with it's more narrow beam width would be a better choice.
I would not install any sort of amplifier.