What impact is it having on other residents? If there is no one affected, what is the issue?
You say “common property in front of their garage”. I wonder if this is like the situation in our townhouse complex, where many lots have dedicated drive in front of their garage, leading to the shared drive.
Visitors, tradies, and even the owners park their cars on this dedicated drive, with no impact on anyone else, and none on access to the common drive. Technically they are parking on common property, but no one else could park there as if they did they would be blocking access to the lot garage.
It seems the same as a standalone house parking in their driveway.