This circuit is off two ways:
- D2 unnecessary. D3 is enough for reverse power input protection.
- Need two I/O pins to control T2 and T3, not one pin driving both transistors. You have to be able to turn the segment displays on one at a time, in a multiplex fashion.
The first can maybe be ignored, the second defeats the display. Problem: If you can't/don't reassign MCLR to be an I/O pin and thus gain another I/O pin to drive the second transistor, this PIC won't work for this design. You'll have to use a PIC with more I/O pins.
As for changing the code, we need the language you are using and the actual code you have (written?) so far. Even then no one may be able to help you with the code.
And we need to know which temperature sensor you are using to figure what values it puts out at the temperatures you mention.
Good luck with your project.
kenjj