Hey luuk,
If you I understand you correctly the problem in your Application is, that you are getting data points from 4 different sensors in one inbox, but can´t differentiate between the sensors, because the data point is not individual for each sensor. Am I correct?
In this case you should use either the IF Column or the IF function ([Beginner] What is an IF-Cell?). Since the structure of your messages is always the same, you are right, that looking into the metadata is the way to go.The key here is to use the information about the topic in the source parameter.
In order to differentiate between the sensors, always check the name of your topic before using any logic.
So e.g. a TIMEAGGREGATE() Function is only used specifically on a message of a certain sensor.
I added a little example I hope this is what you were looking for. 
Luuk Example.json (14.7 KB)
Cheers and a happy and peaceful Christmas to you 
,
Tizian