There is no doubt a local pharmacy or two that will dispense their meds in a pill planner (labeled to low vision). The trick is to find out which local pharmacy that is. Parkinson’s is a disease that needs very timely medicating to minimize the dementia and rigidity, etc., more so than almost any other. The last thing he needs is free lance amateur med juggling~now all you have to do is convince MIL that in her efforts to make things better by monkeying around with dosages and timing she is NO DOUBT making it worse rather than better. Easy for me to say but that’s 41+ years of experience in home health nursing talking. I’ve seen it hundreds of times.
Consider getting them connected with the local Area Agency On Aging. They will have a raft of services and resources to help keep them in their apt and out of assisted living or a nursing home. Building a relationship with that agency for your county before they need more services, it will go better. Even just meals on wheels to start off with. A hot nutritious meal delivered once a day (plus somebody laying eyes on them once a day).