So this parking offender is an owner? And yourself and the other resident rent from your mothers?
It sound to me like a case of “I'm an owner so I can do what I like but you can't” syndrome. This has occurred in my complex on occasion. Owners have seriously thought that the by-laws only applied to those who rent and owners did not have to abide by them because they own the place! Therefore owners could do what they like and renters had to put up with it. And we are talking about educated people here!
And we also have residents who think that if the visitors parking is full (alot of the time with other residents) its OK for them to let their visitors park in front of their garages because a visitors is not a resident and therefore they are not doing anything wrong (even if other residents cannot get past, park in their garages etc). And we do not have a problem with street parking here! And yet………….
Keep taking photos and a diary of offences. If your Mum is the owner perhaps you could get her to take the matter further? You cannot live like that. And no one else should have to either. They cannot do what they want. If you want to park 4 cars at your front door, buy a house and concrete the front lawn.