My father has had unexplained weight loss. Any ideas why?

My dad has lost 30 percent of his body weight in the past year, according to my sister the surgeon. There’s really nothing to be done according to her, and my mom says he eats.

Hes 90 next month, and each family gathering is him giving us old pictures and things. He talks to my sis about which ones he’d like for his funeral. It’s not like anyone wants him to die, but he’s kinda tired.

At 95 your dad just may be tired and is ready to move on from this life to the next. Not eating much or not eating at all can be a sign that his body is just starting to shut down.
With all your dads health issues it may just be time to get hospice on board, and let him be comfortable in his final time here on earth.
Blessings to you and your dad.

There are so many reasons for weight loss that it is almost impossible to list them all. The fact that he is Diabetic and has Parkinson's may factor into it.
He should see his primary for a physical. Make sure that the primary is aware that he is eating less and that there has been a 10 pound weight loss over the past month.

Your dad needs to see his Primary Care Doctor for a medical work up. Rapid weight loss in a man his age can be indicative of a great many medical issues too numerous to go into on an internet forum. Loss of appetite can indicate a wide variety of medical issues as well, so let his PCP have a look-see and try to figure out what's going on with him. Maybe start out with some blood work at his SNF, if there's a traveling lab that comes into the facility, his doctor can write an order for that.

Best of luck!!