“How long do you think my grandpa has left?”

Hello. I am a 19 year old male, grandson to a very wonderful dude. He's a 71 year old male, currently a bit underweight, has a chronic cough, nausea, no appetite, weakness, fatigue, and can't stay awake for more than 2 hours without medication. He has had lymphoma and kidney cancer for a little over 7 years now, and had found it too late to take it out. He's been declining very slowly for a while, but just recently he's been declining more rapid than before. He hasn't had any of the issues stated above until a few months ago, and I'm starting to really worry about him. He hasn't told any of us anything other than the medications he's going on and very little about his health. He hasn't even told his wife, my grandma, anything more than he's told us. I know it's probably not possible to give a completely positive answer, or even an okay answer just based off of this information, but I'm honestly just looking for how long you THINK he'll last for based on all of this. I'm trying to prepare myself for the inevitable, and I think this would give me some peace of mind and a better understanding of what I should expect in the future. Anyways, thanks for the time you took to read this, and I hope you can reply as well. Have a wonderful day, and I hope all is well for you.