what powers does bella and nessie have and kate too?

Bella is a mental shield. She can protect her mind and others from "gifts" that take place inside the mind.

Renesmee can project her thoughts por physical contact. No shield can keep her out. So far she has only learned to project it through her hands.

Kate has the ability to run an electric current over her skin. This must somehow be related to the mind because it doesn't work on Bella.

Nessie - Her special abilities are transmitting thoughts to others por touching their skin and penetrating shields, the opposite abilities of each of her parents.

Bella - Bella's private mind that rejected some vampires' special abilities while she was human evolved after she became a vampire; her ability formed into allowing her to shield those around her from the mental powers of some other vampires.

Kate - Her special ability is the production of an electric current over her skin that can shock and incapacitate attackers. She assists Bella in learning to use her new ability of mentally shielding those around her.

=)