"every body accepts that what has been done is legal and above...

"every body accepts that what has been done is legal and above board" – it is. In fact it's a demonstration of the rules around takeovers. Large shareholders aren't allowed to make secret alliances and pool their voting power. They have to disclose their intentions, which they have here.

"The bidder has inside information and before they put a bid to the board, they go off and make a deal with a major share holder" – the bidder had already made a deal with ENN and Hony before being granted due diligence and they disclosed that fact in their proposal (ann: 3-Apr-2018 Harbour Energy proposal to acquire Santos Limited).

"How can we possibly know if the bidder and majority stake holder have not struck a sweet heart deal on the side?" – They have. This is also disclosed in the initial offer. The other major shareholders (not "majority") have the option to take shares in the unlisted, private company that will be created to own Santos.

"The holding company can do anything it wants in reality" – Anything except compulsorily acquire shares of holders who don't want to sell. If they can't acquire 100% of the shares then they can't complete the acquisition and take Santos off the market. So controlling 15% of the shareholder votes is a signal to any other potential bidder that there's no point trying unless they think they can engage the cooperation of ENN, Hony or Harbour.

"these guys have acted like ... quicker than a bride ..." – Please find a way to express your contempt for the board without expressing your contempt for women at the same time! It says something about that I wouldn't think you'd want said.