Very sorry about your father in law. His situation is horrible, and there is no right or wrong when it comes to the trade-off between the side-effects of a treatment vs the increased life expectancy that the treatment gives.

What the proposed chemo will be will depend on his particular cancer, as well. I expect (although I am not a medic) that it will also depend on his ability to cope with the treatment. So an important question is to know what the side effects, and risks, will be.

I disagree slightly with Denise in that, although she is right that published statistics are often out of date, there is no reason not to accept the prognosis of your father in laws' medical team. The prognosis is always an estimate. He may very well live a longer, or shorter, time than this estimate. But they have years of knowledge, training and experience, and they know your father. They will give a prognosis accordingly.

If you father in law agrees, family members can talk to his medical team, and ask questions, without your father in law being present. This may make it easier to ask 'difficult' questions. Then, when you have gained as much information as possible, you can help your father in law, if he wishes, make decisions regarding further treatment.   

Wishing you all the best. Harry