85 Y/O Male suffering from 4th Stage Stomach Cancer

Dear All,

It was revealed to me 3 days ago that my grandfather has a 4th stage stomach cancer and 50% of the inner lining of the stomach is covered in cancerous cells.
Upon getting futher tests it was revealed that the cancer has spread to some areas of kidney and was touching pancreas.

The docs told us that he has a max time of 3 months.

The time however could be extended by chemo therapy for a few more months. The family obviously wants to take the boat but we havent yet asked my grandpa.

He is 85 years old.
Has 40% of one of his arteries blocked.
Mild diabetes.
and a slight breathing problem.

What i need to learn from here is if there are strong chances of the chemo therapy actually helping him.
Are there any options other than chemo to elongate his life span?
I've seen a lot of articles on Cannabis oil helping to control the cancer spread.. is it really true? (i could not find any legit article that would back up the theory)

And last but not the least.
How do i handle this? Never in the history of our family has anyone ever been diagnosed with cancer or any other serious issue..
How do you behave around the patient so as to not let him feel any more bad than he already does?
Being the eldest on of the latest generation i feel i should be the backbone of the family in such times esp to my dad as he was very close to my grandpa, but its hard.. I am freaking out.. I dont know what to do..

I would appreciate any suggestions/opnions that you guys have to offer.

Please help. :'(