Overgrown trees in Lot property (courtyard)

Our Strata in NSW – pre 1974 (built in 1971). We have back courtyards in 8 of 20 townhouses all these courtyards abut each other.  One owner has 2 very large conifer trees that are spreading into the airspace of lower neighbour so much so one tree is hitting their building and branches growing over their bedroom windows and kitchen window on the lower level. another tree is a camphor laurel is also spreading and over 5m tall. Needless to say it’s cutting out sunlight to this townhouse and the one lower down.  The current owner of approx 2 years has done nothing to either front or back courtyard in way of maintenance both courtyards are overgrown and a mess.  the previous owner whom lived here kept these trees trimmed.  The Strata Committee wrote to the owners respectfully requesting the current owners cut back said trees as they are touching their neighbours building, and cutting sunlight from 2 neighbours further down.  these trees are also now at least 3mtrs over the driveway of next door, we believe that that strata is sending a notification to our strata to have these trees cut back.  The committee has asked the Strata Mgr to contact them which they did and the owners say its OC responsibility as the trees are over 3 metres and their lawyer told them.  On our strata plan we have wording ‘the boundries of the open courtyards are limited to a height of 15ft above and a depth of 10ft below the ground floor level of the respective lot immediately adjacent to the Open Courtyard’. 

we have a bylaw in place (our own bylaw) – which reads
Special bylaw 1.

 the owner of a lot must maintain any part of his lot that is visible from outside the lot in a state of good and serviceable repair, and keep it clear of rubbish and in a clean tidy condition.
the OC may carry out work that is required to be carried out by an owner  pursuant to this by-law and may recover the cost of doing so from the owner as a debt.

these owners are giving push back and ignoring the requests to cut back.
do we ask the Council to come and inspect these non-native trees?  would this help.  and would they put an order to trim.
on NSW fair trading website it says if the trees are on common property it’s OC, if trees are part of your lot you are responsible as the owner.  

with the bylaw in place can the OC write yet another letter to have the trees cut back and if they don’t the OC will engage an aborist the cost will be added to their ‘account’ with the strata mgr.

these trees are now approx 5-6 mtres tall

thank you