Thanks for all your good advice. The solution with connecting them in parallel I already had figured out for myself. I wasn't sure whether that actually worked so i did the experiment. And it worked fine!
It is by the way for a lab experiment.
What material should I use for soldering them...
I am looking for a unit which can simulatnaeously measure 3 k-type thermocouples, average the two which are the closed together (and thus rejecting the one which is furthers off) and control a heater unit to bring the temperature to a certain setpoint.
We already have a control unit to control...