I agree with waterloo that you need to take care of yourself first. If you are not rested and energized, you can't help others. You need to put your health first.
Let me step back and say that I am a person with Parkinson's - not a caregiver as you are. I empathize with, but have not experienced first-hand, your situation. Caregivers are angels.
It sounds like you have two issues: 1) grown children whose life choices you feel responsible for, and 2) a spouse with PD who needs a caregiver. (It's SO easy to over-simplify when you are on the outside looking in. I know your situation is not as easy and simple as this sounds.)
You are NOT responsible for your grown children. At some point they need to take responsibility for their life choices. It may not be pretty, but it's not your fault/responsibility. Therefore, you may offer guidance, but are NOT responsible for and should not feel the need to 'solve' their issues. You only have so much time and energy. You need to prioritize and set boundaries with your children. I guess that's it, you need to set boundaries with your kids - especially the older ones. There are some great books on setting boundaries.
On a different note ... I don't know whether you live in a metropolitan area or not, but sometimes there are adult day care facilities where your husband might be able to go one day or more a week and free you up for a day. I don't know whether there might be financial assistance or any PD or other support groups that might assist with the financial aspect. I would encourage you to find out whether there are any PD - or other - caregiver support groups. Support groups can be a wealth of information. Or groups who are resources on senior citizen-type programs. Check out your local phone listings or online is even better.
Again, it is SO easy for me to oversimplify. You need to look out for you. I hope you can find peace because it sounds like you are about to implode. Best of luck!
lizzy4451