OK just read your original post again and have the feeling it's all working perfectly correct:
The thermistor is placed between 5V and A1 and i have a 10k ohm resistance that goes to ground and the problem is that when i place the thermistor on pin A1, the value on pin A1 is around 500 which is correct but all the other pins (A2, A3, A4) are the same value but 5-10 units lower than the previous.
The Arduino has only ONE ADC, which is multiplexed. An ADC contains a small capacitor. When you read A1 the ADC connects to pin A1, the cap charges to the pin's voltage, and the value is read. Then you read A2, the ADC connects to pin A2 (which is not connected), the cap voltage doesn't change really (a little parasitics of the pin itself), and you get about the same reading.
So that's that.
I have a rezistor divider but it's between analog pin 1 and ground which makes it a pull-down, i assume, so i tried with a second ntc and a pull-up which seems to work but not really, because the value goes down and using Steinhart-Hart equation would reverse the temperature readings.
Normally NTCs are wired between GND and the pin, and a resistor between pin and Vcc. So if your temperature goes the wrong way, maybe you have to switch them?
The goal is to have up to 5 NTC thermistors and measure 5 different temperatures but i can't find anywhere some reliable information and schematic to show how to do so. So if anyone knows how to do it i would appreciate it.
You know how to connect one. Connect four more the same way. Done. There's really nothing more to it. A thousand thermistors, OK now it's getting interesting.