It sounds like a fairly straight forward scenario with the right sensors and apps. There are a couple of sensor available which have temperature and humidity in them. Three popular ones are Monoprice 4 in 1 sensor and the ZooZ 4 in 1 sensor and the Aeotec Gen 6 multi sensor. These have humidity, temperature, lux and motion sensors built into them. You can reduce the sensitivity of sensors you don’t want to use to increase the battery life (which can vary from 3 month to a year depending on the sensors in use).
Since these are split A/C units I’m guessing they aren’t integrated into SmartThings as a HVAC or thermostat unit. If so, you’ll need to connect some Z-Wave or ZigBee outlet to the power sockets which can then be used to turn on / off. You’ll need an app which support managing climate using switches rather than thermostats to use these units to manage your temperature and humidity.
Here are some example of apps which can manage climate using a Thermostat or a Switch, each one has a slight different functionality based on what types of automation you’re trying to create for your climate control. Some have advanced features such using a motion sensor to trigger the climate control (your multi sensor motion sensor can be useful here).
[RELEASE] Motion Sensor Thermostat with Remote temperature sensors, Presence detection and Schedules