I've looked on Google, the official rules for Table Tennis, and on this website but found nothing telling me whether it's illegal to use two rackets to play table tennis. I understand there are rules which states there must be a "free hand" during the serve, but during ongoing play it is legal to use two hands to use a single racket or switch hands with the racket during an ongoing point.
Lastly in the rules they always say racket rather than racket(s), but it would seem somewhat unnecessary if they had said racket(s) seeing as no one actually uses more than one racket and it's too niche.