Ask around and see if anyone you know has a possum catching cage.
We borrowed one to catch a stray Tom Cat that had been living on our farm for 18 months. I usally don't mind strays but he was a real bugger for getting the dogs barking or wailing under our house where we couldn't get to him.

We eventually catch him and he was real nasty. Yes he was put down but that was a much kinder fate in my opinion as he looked in poor but well fed condition.

I would catch them and them take them to the RSPCA and who knows they may be chipped and returned to their owners.

Nae x