To make a character believable you need to create them from scratch, but also give them opinions and points of view. The writer must stand in the character shoes (so to speak) and write from the character's point of view.
It is easy once the Character Profile is done. You can create a situation and put your character in it. He or she will react from the profile that was given to them. But to create a point of view for the character, you must become that character/s. Think like them, and develop a belief system. By adopting the character point of view, you have constructed an exchange of honest and powerful emotions of human beings. Since each character/s will have their own set of believe systems, they will also now have a point of view.
A good question to ask is:
How would I react if I were this character/s with these belief system/s and point of view?
By standing in your character/s shoes and acting out truthfully to their profiles and belief systems, it will be easy to give them a point of view. Good solutions for exploring all possibilities with your character/s, are to try all different approaches and circumstances. You will come up with something that you feel comfortable with that is very believable.