So how do you expect people to move their possessions in and out of the property?
While parking in the driveway is an inconvenience when planned properly it is minor. Also, moving in and out of apartment blocks is common.
It seems you have a blanket ban on anybody parking in the driveway. Have either of the resident owners ever needed to have a delivery and blocked the driveway even for a short period of time? If so were they spoken to the same way?
Noting there appears to be no legal way of parking and removing their goods the departing tenants took the path of least resistance and just broke the by law knowing there was very little in a practical manner you could do at that time.
Perhaps develop a by law for how to handle departures and arrivals covering planning and advising the other residents of when and how long.
This situation is a bit of bull headedness on both sides but I actually have more sympathy for the departing tenants. You made their life harder than it needed to be and paid the price.
Plan ahead for the next resident transition and have an easier time.