why does alice's and jasper's power work on bella but noones else works??

Because they don't involve her brain. Her power is a mental shield. Alice's power doesn't involve anything mental and same for Jasper. Edward and Aro can't read Bella's mind because they read your mind. Jane's power won't work because it's mental pain anda feel. Hope that helps! :)

Alice's power doesn't involved anything about mental...- yes i agree to that but not with jasper's because his power has something to do with controlling of emotions so i'm not buying the excuse that his has nothing to do with brain. emotions are somewhat connected with brain activities.

Emotions are thought to be related to activity in brain areas that direct our attention, motivate our behavior, and determine the significance of what is going on around us. emotion is related to a group of structures in the center of the brain called the limbic system, which includes the hypothalamus, cingulate cortex, hippocampi, and other structures.

Long story short, Alice sees something physical happening, not the reasoning behind it. Jasper's mood control affects the body physically not mentally (i say this because the people affected know they should feel one way, but are unable to feel that way until they are away from jasper's control). Edward reads minds, as does Aro, and Jane's power makes a person's mind believe that they are feeling pain. Bella has a mental sheild. She will not be affected oleh any supernatural power that affects the mind. However, when it comes to the physical, she has no defense.