Sorry to hear the prognosis. There is no wrong answer to the choice you make.
The bone marrow transplant is usually done after a chemo that is very strong. Chemo kills fast replicating cells like cancer and bone marrow. They usually have to limit the chemo based on a patients blood cell count. It can wipe out all the white blood cells leaving them open to infections. In this case they will use a chemo that will probably kill all his marrow and hopefully all the cancer, but before they do, they take some marrow out and after the chemo give it back to him.
My prayers are with you and your family. Be sure to take some time for your wife and yourself. This is never easy. Mike