jureivis:
It is certainly at least Arduino compatible because it is mounted on Arduino Mega (it is not visible in the picture but if you have doubts - i can make a picture of a back side of device).
Apart from the words "Mega power supply", which could be meaningless, there is nothing on the data sheets that even vaguely suggest it has anything to do with Arduino, and quite a lot which suggests it hasn't - .like 48v wires. Information on how it connects to Arduino would be more informative. You really need the programme that is in it too but, once you have sorted the connections out, you might be able to write a new one. I believe the screen is one popular on Arduino, so there should be no problem with that.
And what makes you doubt that it could work with 3 sensors? In a scheme attached (pdf) you can see three sensors plugged ???
I don't doubt it will work with three sensors. I do doubt you are going to get it to work - with any - but, if you do, it is likely to work fine with five. This would surely be the case if it polls the DS18B20s by index rather than stored addresses.