Welcome to the forum @StefanH
I took the liberty to edit your post to mark your sketch as code. This makes the code mich easier to read. You can use the </> button on top of the edit area next time.
Have you looked at https://github.com/mysensors/MySensorsArduinoExamples/blob/master/examples/DallasTemperatureSensor/DallasTemperatureSensor.ino ? It has support for multiple sensors.
In any case, please post the debug output of your sketch. It will make it 10-100x easier to troubleshoot. If you haven't already, see https://forum.mysensors.org/topic/666/read-this-first-it-could-save-you-a-lot-of-time/ for how to enable debug output.