Should I encourage him to get up or let him be?

3kids, sorry this is happening... the shuffling gait can be parkinsonism and may respond to medication or other treatment...his swallowing might be affected and a speech or occupational therapist can evaluate that and maybe recommend a different diet and some nutritionist consultation. "Just aging" is NOT OK as a diagnosis, it does not sound like you have a suitable doc unless you and dad really want to go the route of benign neglect and let him go straight down hill. Just because he does not want a colonscopy may or may not be reason to forego all diagnosis and treatment of anything that might give him a better quality of life. You would be looking for a geriatrician, neurogeriatrician, or comprehensive geriatric evaluation...

If he had large tumors I would have expected those to have shown up on the cat scan.
DO keep him walking if at all possible - laying in bed easier short term, but causes body pain quickly, not to mention weakness & care issues.
I'm sure you've tried all kinds of things, but these are all the things I can think to suggest in random order;

Food;
Ice cream -- if you can, spring for the good stuff - Hagen Das has 270 calories per serving, and its all "food" - - cream, sugar, egg yolks. Not great for those of us who DON'T need weight, but easy to eat for those who need some extra.
Concentrated nutrition -- mal-absorbtion sounds right, though only eating 1/3 of normal not good.-
Maybe gut bacteria out of whack? If you haven't already, add some yogurt, kefir, "live" saurkraut, those little yakullt bottles, anything that might repopulate the intestine with good bacteria (yougurt can be 1 Tbsp 3x day - doesn't need to be much if he doesn't like it). Amazing how many docs forget to mention this after antibiotic treatment (but VETS remember - crazy!)
Daily multivitamin & especially vitamin D & B-complex (some people swear by b-12 injections -- might be worth a try, as b-deficiency is common. Not much to lose, and it IS hard for the elderly to absorb from diet - heck the placebo effect alone might be worth it).
Frequent snacking with some redeeming nutrition - if it's peanut butter on crackers, etc in small amounts it might go down OK.
Add butter or oil if his stomach will tolerate it --
Beer, if he likes it & no reason not to (odd, but has calories )

"bikeless" exercise bike -- these just have the pedals with a stand-- small, sit down on regular chair & pedal. The kids can have fun taking turns too -- cheap.

You say he's too proud to use a walker. That's a shame. After several serious illnesses, I now have mobility problems and must use a walker or a wheelchair. Without the walker, I would hardly ever get out of bed. I have one of the walkers where you can sit down on a seat if you get too tired or dizzy, and it's a big help. Please see if you can explain to him that using a walker is not something to be ashamed of and that it might really help him.

I understand you feel he seems to be nearing the end of his life, so it seems pointless to push him to get up. I have days I feel the same way with my mom. The problem with letting them stay in bed is that it will involve a whole new level of care and physical decline. It is so much easier to bathe, dress, and toilet someone who can walk and assist, even if only in a limited way. And becoming totally bed bound can lead to pressure sores. It also isolates him from you and the outside world. I think you should encourage him to be moving and active as long as he is able.
My mom benefited from some very simple exercises shown to us by a physical therapist, and of course uses a walker. I wish I had some advice about his stomach issues, it is frustrating when doctors can't put a name to the problem.

My father had a touchy stomach. He didn't like the big family meals I cooked very much. He preferred finger foods. He liked scrambled and boiled eggs because they were easy on his stomach. He would also eat salads without salad dressing. He fluctuated between constipation and diarrhea, but in his case I think it was a Miralax thing. He would be constipated until he had a dose of Miralax, which would cause explosive diarrhea for him. He also had dizziness, which didn't help his tummy at all. We learned in his final days at the hospital that his stomach was inflamed. The hospital thought maybe it was viral, but didn't say for sure. So much was wrong with him at the time that it was just one more thing. I wonder if your dad has some inflammation going on and if there is any way to help it.

When my dad went down to nothing, he decided to get out of his bed and grab an orange. He was so weak that he fell onto the ground and broke his hip. That's my concern is his weakness and mobility issues, among the malnutrition. Please talk to a doctor about that and maybe they can give him supplements. My dad tried Ensure and all that chalky crap --- he hated it! It makes you more nauseous than anything. BUT -- he LOVED Slim Fast. I have no idea why -- but he chugged them down and he felt better. Try that.

About sleeping in on mornings... My mother tends to do that now. She's in such pain, between her colon cancer and her sciatica pain, I let her sleep in a and I serve her coffee and breakfast inside her room and she eats and then has the strength to shower and go on about her day. But I would definitely let them sleep in. They're tired, they're in pain............ but make sure that they eat and get up and outside if it's nice out just to get some air.

Good luck with everything!

He eats about 1/3 of a regular portion of food.

Thank you Jessiebelle. Yes, that's what i feel like. He's not keeping any nutriants. We've done ensure, i give him ice cream, three meals a day and he's been "sick to his stomach" every day for over a year. I look up malnitrition, body wasting constantly. Just trying to understand. It always says after a elderly has a rapid weight loss like this die to such, such and such. I guess social, phycological issues, dental issues ect.. they are at a higher risk of early death, frailty, falls ect.. I don't want him to fall because he has no room to lose weight being hospitalized and i feel like that wpuld just be the end. However we havent discussed a walker, or anything because hes just too proud. Hes shuffeling, but at least hes walking on his own im sire he feels some sense of pride. Its a hard thing, i have three kids so following him around his every move is not something im ready to do. But if a fall is the end, i feel guilty im not Doing something. So i do let him sleep. Where hes safe. Maybe im wrong, but thank u im not alone.

my3kidsok, I have a mental formula I use when trying to decide whether to let my mother stay in bed or not. My mother likes to sleep through the morning. I have tried to get her up several times, but she normally resists. So if there is nothing to do and trying to get her to get up cuts into my work time and lowers the quality of my own life, I let her stay in bed. I'm sure many would disapprove of my methods, but for me this is a marathon and not a sprint. My sanity is very important, so I don't want to waste too much of it trying to get her out of bed in the morning. I would say if your dad does not feel like getting up and there is nothing for him to do, just let him do as he chooses. I do wish the doctors could find out why he is wasting away. That seems to be the primary problem. It sounds like he is dumping, instead of absorbing, his nutrients. Is his appetite still good?

ps the doctor has no prognosise for us of what is going on other than aging. He did have life changing situation to caise weight loss. But the constant stomache aches, diarreah. His doctors want him to do one of those up the butt tests, for cancer is what they are reaching for. But he doesnt want to. The cat scan didnt show anything. I feel its that malnutrition, scarcacia is it. body waisting, but how long can he go like this. I dont know