The first problem you have changing the visitors parking into “other “ parking.
The building approval by the council was based on the premis of a certain number of visitor parking spaces. In order to reduce the number of visitor parking spaces will require a DA approved by the council . Good luck getting that approved as council requirements are more stringent today. Without council approval every other step is academic.
Check what type of resolution is required for what you propose. Most changes to use of common property require a unanimous resolution. Your elderly resident could vote against your proposal and you’re back to square one.
The “sharing” of these visitor parking spaces is just going to cause more future trouble. People, rightly or wrongly, will claim others have unfair access or use of the spaces. Someone is going to sort this out, and neither the police nor NCAT are going to help you because no law has been broken.
If you can get the visitor parking spaces reclassified, then consider auctioning off the spaces . Maybe make a yearly lease for each space and rent the spaces to the highest bidder.
You may suddenly find that owners are not prepared to rent the parking and find somewhere else to park.
Finally your SM is correct. You have to present in court with clean hands. Until the current mess is cleaned up, your elderly owner will quite rightly claim he is being victimised, and until a clean pair of hands is presented in court, the courts won’t enforce a judgement against him.
Finally remember the police have no jurisdiction in terms of parking on common property. They will quite rightly say it’s a strata issue.
Parking on common property is covered by a by law and so it’s a civil and not a criminal matter