You have both moved house around the same time. Did you decorate the houses before moving, or immediately afterwards. Especially did you use stuff like gloss paint, undercoat, floor sealants, etc - the smelly things, with solvents.

Did the gardens require a lot of work, i.e. did you use weedkillers, defoliant type ? Scotland? Did you spray for midges?

Agree with Aunt Bean on carpets, new carpets/carpets cleaned with solvent type cleaners....

In the time you have been there did you get a virus type illness around the same time? Even something fairly low level, cold, flu etc.

Does anyone else you know in the area have PD? Maybe your GP might have noticed if he/she has unusual amount of patients. Most doctors only have a scant handful.

Were there any unusual environmental events in your area?

Do you have a source of high output electricity adjacent to your homes?