How to cook Mixed grains all together in one pot
Some of them aren't grains, and they'll be the limiting factor.

In particular red kidney beans must be boiled for a good few minutes to remove phytohaemagglutinin. If you treat the whole lot as beans, you won't go far wrong, though the actual grains are likely to end up rather soft, a short of porridge with beans in. This is probably intentional.

So I'd soak overnight, then boil hard in fresh water for long enough to make the kidney beans safe (sources vary from 10 to 30 minutes). Then I'd drain and slow cook on high with whatever flavours you'd like for 6-8 hours, or simmer gently for a little less time. Alternatively you could pressure cook them.