side1 setFriend [side2 , value];
eg : to set independant allied to west :
Resistance setfriend [West,1];
(turn the value to 0 to set them enemy.)
if you place this code into the init line of the unit he will be the only one to be friend with west, you must add it for each independent units you want to be friend with west (blufor).
if you want this code to apply for all present independant units without the need to edit for each present units, place the code into the init.sqf of your mission.