> Under what pretence would they grab Ambani's property?
If there is no existing law, government can make laws. I mean the government did nationalize so many banks at once right? The government is sovereign. The amount of power it holds over it's own people, even the richest ones, is far far higher than what it holds over another strong sovereign state.
Anyways this was all about power. There are so many other reasons for ensuring someone in the country holds the wealth rather than your competitor.
No. The Enemy Property Act, 1968 is specifically made for Pakistani Nationals after the 1965 Indo-Pak War. It is not generic. To declare China as an Enemy a proper War should take place between India and China. Is China ready for such a misadventure?
If it wants to maintain the appearance of being lawful and fair, there is already an Enemy Property Act, 1968 to more or less support grabbing Chinese investments (perhaps with an amendment or two). Under what pretence would they grab Ambani's property? There is Eminent Domain in India, but only AFAIK for land ownership, and even that requires fair compensation at market prices.