Answer:
From a Kantian perspective, the haves would not be justified in having more than they need if it means using others as a means to an end. Kant's respect for persons principle requires that we treat others with dignity and respect, and not exploit them for our own benefit. Therefore, if the haves are benefiting at the expense of the have nots, then they are not acting in accordance with Kantian ethics.
In terms of moral obligation to share, Kant believed that we have a duty to help others, but not out of a sense of obligation or duty. Instead, we should help others because it is the right thing to do, and because we recognize their inherent value and worth as human beings. Therefore, from a Kantian perspective, we do have a moral obligation to share, but it is not based on a utilitarian calculation of maximizing happiness for the greatest number. Rather, it is based on a recognition of our duty to treat others with respect and dignity.