Driving mosfet in battery balancing circuit by an mcu
A low-part-count solution would be using an optodriver such as the TLP190B, which allows you to drive a N-FET referenced to a different potential than your local ground without the need for an extra isolated supply. (The IC works by illuminating a small LED that points at a small photodiode, generating the current to enhance an N-FET's gate).

A possibly cheaper (but higher-part-count solution) would use N-FETs to pull down on the gate of P-FETs. Depending on your P-FETs and how many batteries are in your stack, you would need to be clever with the inclusion of zener diodes to stay within the V_gs,max of the part. The scheme I'm suggesting might look something like the schematic on this page.

Finally, there are a whole slew of battery management ICs that would work, depending on the constraints of your application. Searching for a "two cell battery management ic" would put you on the right track.