I totally understand what you are going through. In January 2007, my 77 year old Mom was diagnosed with lung cancer. Due to her other medical conditions she was not a candidate for surgery, so she underwent a long round of chemotherapy and radiation. It took a big toll on her, and unfortunately, in January 2008, it had spread to her brain. She received whole brain radiation for that one, and it was devastating to her, physically. There are no further treatments for her, so we brought her to my brother's house to live out what time she has left surrounded by family and friends. Saying all of this, my advice would be to keep him surrounded by family and friends as much as possible, accept help from a hospice organization, if you can, and make him smile whenever you can. We have been assured that she will find peace when the time comes, and we can only do our best to give her peace while she is still with us. Also, take care of yourselves, and do some "normal" things when you can. You will burn yourselves out, otherwise. Good therapy for me is to be around babies and little children as often as possible. It is reassuring to remember life is still going on, and not just focus on dealing with someone coming to the end of their life. It is a sad time, but try to remember the life they lived, and the love they gave you, and give it back to them now, when they need it most. My thoughts are with you and your family.
Sandy