How can I keep stable position of my drone? How can I detect bias of them?
With a..


3 DOF (Degrees of freedom) mems (Accelerator) you can calculate the angles (if your drone is stationary).
3 DOF mems (Gyroscope) you can calculate the angles (this will drift)
3 DOF mems (Magnetometer) you can calculate the angles (which might be distorted by large heavy/soft iron objects)


If you take the information from all 9 sources = 9 DOF simultaneously you get something called sensor fusion (wiki), Here's a tutorial about this at adafruit. 

In an ideal world where the fusion works perfectly, you end up with something called AHRS (wiki) (not arse) which stands for "Attitude &amp; Heading Reference System". 

AHRS modules used to be very pricey, but just recently, about a month ago, I came across the GY-955 module (aliexpress) which even comes with integrated kalman filter, the kalman filter gives a good estimate for what the real AHRS value actually is. 

I haven't tried the GY-955 module so I can't say how good it is, or if it's just Chinese bogus marketing. But if I were you I would just take the easy route and acquire a GY-955 module and call it a day. 



If you want to keep the drone geographically stable then you will most likely also have to add a GPS module to it, or some other sensor that relates to the physical real world.