Thanks, I had thought of that but was not sure if the heat pumps would be sufficient in the Texas heat and humidity. The existing ACs are only 2 years old and SEER 16, but I see your point.
Heat pumps have never struggled in the heat. A(n air-source) heat pump is an AC unit that has been upgraded to heat in addition to cool. Modulo the very far south of the lower-48, and HI, your cooling load is going to be less than your heating load. You can approximate* this by taking your target temp (call it an unmustachian 70 year round) minus the outdoor temp. You can think of that as a hill that the heat pump is trying to move the heat up. If it gets as hot (air temp, not heat index, the heat pump doesn't sweat like us humans do) as 110 that's a 40 degree difference. So that's equivalent to a 30 deg F winter, and there are *lots* of places that get those temps or lower.
My climate in the midwest looks more like an average low of 20 (-50 delta) for winter and 85 (+15 delta) for summer vs a static 70 deg.
Now, the one thing with tenants is you should make sure to give them a heads up about a heat pump -- their bills will be higher in the winter than the summer. Make sure they're prepared for that, because what you don't want is they can either pay rent or power but not both. If they don't pay rent you lose. If they don't pay power and pipes freeze and burst, you also lose. I don't like lose-lose situations.
*: Approximate, because it isn't just air temp, but also solar load, which helps in the winter and hurts in the summer and depends on a lot more factors -- insulation, design of the building, trees, etc.