Most modern receiver front-ends have minimal filtering, just a wide pass-band filter and the IF filters which reject the adjacent channels more then channels further off frequency.  If you have more than -30 dBm showing up on any antenna regardless of frequency spacing it'll probably cause problems.  150 ft is only ~45 dB of isolation, so if you're transmitting with +45 dBm (32W) less 2 dB of duplexer loss, less 2.5 for cable loss plus 3 dB for repeater antenna, less 45 dB of isolation plus 3 dB for rx antenna gives about +1.5 dBm which is definitely going to mess up a receiver unless more filtering is used.  You can play with filters to see what works, but I suspect you'll need two notch filters to get that down to something that doesn't effect your receiver.

You need to hook the system to a service analyzer and see if it's actually over modulating, it's doubtful unless you've injected audio after any limiter circuits. Running the math it's probably front-end overload, you'd be best to notch out the transmitter on the effected receivers, you may have to put a pass filter (and/or notch filter) on the transmitter too to remove some sideband noise as well, maybe not if it's a clean transmitter. It's usually a good idea to have balanced reject filtering on both your transmitter and receiver.

Jesse