Chiuchiu shows up as red but Google says it's fine?
maybe there is a time offset between the readings from the two sources. Other factor could be the quality of the sensor itself or how google manage to get that data.
Also, what bounds this to Chile? It seems that using location coordinates and standardising the fields on each sensor type may help unify data from any weather station.
Regarding your second question, idk really, if there is public data from other countries it could be formatted to a common format for the app, it is a nice idea, ty.