OK, shelve that idea. Okay, take it all equally seriously. It's their money, after all. Just do what each one says you should do. Try this, reverse course half-way and try that.
Work grinds to a halt.
Nothing gets done. No, that doesn't work either. Option 3 Ignore what everybody says. This might actually work if they all have lousy memories, if they're just venting. If what you finally deliver is so brilliant, so overpoweringly successful that they're blinded by its sheer brilliance, they'll be so busy taking credit for your work that they won't remember that you ignored all their suggestions and criticisms.