I think the issue would mostly be solved by adding the cost of any marques to the purchase price of the parent if you try to acquire it. A more refined option (feature bounty?) could be to have a menu to choose to buy only the parent and spin the marques off or let others buy them.
Edit: Okay, it seems as if either the parent or one of the marques had 300 million in debt which I somehow overlooked... this may prove interesting.
Edit: Okay, it seems as if either the parent or one of the marques had 300 million in debt which I somehow overlooked... this may prove interesting.