How to connect Li-ion batteries with thermistor pin in parallel?
The accepted answer is very dangerous for reasons as I described in the comments of the wrong answer.

To correctly and safely handle the NTC (=TH) pin, ideally the charger should always see the hottest battery, whichever it is. The problem is, at start we don't know which battery will get hot. This unfortunately requires a small circuit that takes both NTCs (one for each battery), and selects the correct one to forward to the charger dynamically. This boils down to selecting either the lead with the higher or smaller voltage of both.

Unfortunately, the "hotter" NTC lead can be either the lead with the smaller or higher voltage, depending on how the temperature measuring circuit inside the charger works.

If you cannot figure out how the charger measures temperature, or you cannot build the circuit necessary to connect both NTC leads, you should remember that with at least 50% probability you have no temperature protection at all, so you should not leave the batteries unattended during charging.