I'm afraid that both ZGL and ZIGV shares (if you can find a buyer) will likely continue to trade at a discount while being controlled by the Sim family. Nepotism is not bad per se. It does raise a few concerns. Philip Fisher noted in his book that "without breaking any laws, the number of ways in which those in control can benefit themselves and their families at the expense of the ordinary stockholder is almost infinite".
The Sim family will likely want to keep its reputation intact. As minority shareholders we can possibly remind them that unreasonable channelling of profits to themselves may make them wealthier, but it may come at the expense of their reputation.
