If they are willing, they can add you to their trusted list, but since they are a WikiTree user, they would have every right to not want to add you just because you might be a near cousin. Typically, most people choose not to do this, but where you are personally connected to them (live nearby, call them on the phone often, know them "personally") then there might be exceptions. Under those circumstances, they might even make you PM and you could co-manage that profile together.