The Who's Who Caper Doubletake Series Book 1 by Lee Duran

Two women who look enough alike to be twins--and so different in personality that they might be from different planets--meet by chance and decide to change places for a week. Each will perform a task the other dreads: Samantha will deal with a "dying" grandmother and Jayne will sign Sam's divorce papers. What could possibly go wrong? Everything, and in bunches, including someone on their trail with evil intent. But who's the target? And will they live long enough to find out?