My mom does, but she works overnights a lot. My grandmother's sister is 15 minutes away. When the weather is OK, she takes my grandmother to her appointments, but she lives outside of Chicago, so the weather is rarely "OK" in the winter months.
The shakiness and unsteadiness you're describing in your FIL is how it started with my grandmother. It is worth it for him to get diagnosed sooner rather than later, because you can delay the progression somewhat with meds. She was here in the summer and a few times, she would need to sit down immediately and someone would have to help her to the nearest chair. I thought it was something else, but that was the beginning, I guess. When I went to her house for Thanksgiving, she was using a walker and out of nowhere, she would need to sit down and her right hand would start shaking vigorously. My mom has been telling my husband she thinks I am not helping out enough, but I don't know what I can do other than visiting for a week every month or so. I can't move in and fly back to NJ at the weekends, you know? I didn't choose to move away. This job in NJ was the only job offer my husband received after being let go.