Turn the money tap off now. The reason your son has been able to indulge in these fantasies and avoid knuckling down to a proper job is because you and his wife have paid him to do nothing. How many people would work if they could stay at home being paid to do nothing but live in cloud cuckoo land?
I read a novel recently, which featured a similar character and when someone turned him down the femal relative whailed, 'What will happen to him now? He will starve. The response was that 'A short course of starvation would do him good'
This is my response to this conversation. Stop giving him money, let him face up to his debts and the need for im to pay them with money he has earned. His wife should also do the same.
By the way, he hasn't been let down so often by investors, they have either investigated his plans and decided they were not any good, so declined to support him, or they are part of his fantasy, fictional investors, who he met in a pub and who said polite things about his plans and bought him a pint.