Currently, the GrovePi does not support 1-wire sensors, like https://www.seeedstudio.com/One-Wire-Temperature-Sensor-p-1235.html?cPath=25_27.
We plan to fix that!
According to https://www.seeed.cc/Hot+Water+Solar+Boiler+Project-p-170.html “multiple One-Wires sensors can be hooked up to 1 digital port on the Arduino”. There are no more details, but it makes it sound simple.
@donblair have you looked into this at all?