My solution is to add some more smarts, additional controllers. You could use some inexpensive Raspberry Pi zeros or even cheap Arduinos. This will get you started with a system you can expand easily. I would connect the sensors to the zeros and add a CAN link. CAN is time proven reliable and will operate over long distances. MCP2515s are inexpensive and do most of the hard work for you.
The communications can also be accomplished by WiFi, LoRa or many other forms of RF communication. There is a lot of information for DIY using either of these with the Pi or Arduino.
However since you are looking at cabling between locations consider using a 4 conductor cable where 1 pair supplies 24VDC and the other pair is CAN. Using a SEPIC (Single-Ended Primary-Inductor Converter) converter (I am partial to them) at each zero (this cleans up the power and keeps the current on the power feed down) you should get a very reliable system without a large cash outlay.
This network gives you a lot of future capability such as alarms and controls at the remote buildings etc. You can expand it at any time by just adding another node. This keeps the sensor lines short and reliable.