Problems in design of a BLDC motor driver
The issue is the drive stage &amp; using all Ntypes 

You are using TC427CPA as your drive chip who's supply rail is the same as your DClink.

To turn on the upper MOSFET's the gate voltage must be a minimum of Vth about the source. To fully turn on the MOSFET (lowest impedance) the the gate voltage must be a lot higher than the source (refer to the devices datasheet) 

Without getting into instantaneous specifics... Imagine you are wanting to turn on any of your upper N-type. The source potential would ideally be equal to your Vcc... however that is the voltage you are supplying the gate with, thus the source can only be Vcc-Vth lower for any sort of conduction. THUS the upper MOSFET's cannot be in saturation but in some linear, high resistive state and thus will get hotter when power is drawn via them. 

The simplest solution since you are working with v.low voltage is to replace all the upper devices with P-Types &amp; change your code to deal with the needed inversion