The best way to do this is to use:
PedSetTypeToTypeAttitude(faction id, faction id, attitude) which each of those is a number.
I don't have a complete list atm of what does what for each number.....so what I suggest is experimenting and see what happens.
attitude is 1 to 5 if I remember correctly. I could be wrong since I haven't looked at this for a while so I may have forgotten something.