Turning potentiometer changes other potentiometer's value(STM32)
One technique I've used to minimize this effect is to sample an unused channel tied to ground in between sampling the active channels.

The resistor values you are using are on the high side. I haven't specifically used that processor but on other devices, it is recommended to keep the source impedance to less than 10k ohm.

It can help if you add a capacitor to ground at each input - since the signals are very slow you could use up to 0.1uf with no problem. This will provide the charge needed to transfer to the sampling capacitor within the processor.