AVR-Chat

>
>To fully turn on the upper MOSFETs, thier gate voltage has
>to be a 6..12 volts higher than the voltage at thier source.
>
>So you will need an isolated high-side driver for the two
>upper MOSFETs.

Generally true, but check the specs on your mosfets, some are lower than 
others.
The 2N7000 is a notable exception, it's compatible with CMOS logic levels.