What can one expect from a Parkinson’s/dementia diagnosis?

When my uncle got parkinson's, he said he went to the last chapter of the book and it didn't end well. He started eating slower and slower, couldn't button his shirt, took hours to shower and get dressed, had to wear a bib to protect his clothing, etc. As it progressed he started with dementia and got a bit mean/violent, had hallucinations and ended up in a home.

Every patient is as individual as his or her own fingerprint. Your question is best addressed with the physician who has diagnosed the patient. Your diagnosis and prognosis will come from that doctor, but do know that even for doctors, the progression of a disease is unable to predict with accuracy.
Meanwhile, with a new diagnosis make use of the world wide web and any organizations with support groups. You will at the least be able to form a set of questions to ask.
When first diagnosed it is a shock. It takes time to research, to do things one at a time. Hope you will come back with specific questions for us.

You might want to contact one of the several very helpful Parkinson's organiztions for a more detailed response to specific questions. They could also connect you to caregiver support groups. These organiztions include the American Parkinson's Disease Association, the Parkinson's Foundation, and the Davis Phinney Foundation. You can Google them for their websites and phone numbers. Also you could contact the medical provider who has made these diagnoses. Parkinson's is a progressive degenerative neurological condition that manifests in many ways. A minority of Parkinson's patients get Parkinson's related dementia.
Do you have some more specific questions that we can help with on this site?