-5V to 5V DAC Design
Won't work. You need to drive the ends of the 2R resistors push-pull from +5 to -5, not just to +5, so you need something like complementary MOSFETs and level shifters. 



Edit after 2nd schematic added- since Vdd is 3.3V you need a more complex level shifter. Maybe something like this: 

R2/Q2 could be replaced with a logic level MOSFET- 2N7000 is a bit marginal at 3.3V. 







simulate this circuit &ndash; Schematic created using CircuitLab

Unless you are doing this for educational purposes it may be better to just buy a DAC. Of course you could also use a high-Z R2R ladder off the MCU and use an op-amp to shift the 0-3.3V output to +/-5V. Plenty of answers here on that sort of thing.