Largish cage sanitised with dish soap to get rid of any possum/other cat smell lingering from the last use. Especially important that bit as fear/stress smell lingers and will warn them not to enter the cage. Bait the cage with tuna or sardines right at the back. Let them eat in there for a few nights without trapping them. Regular dry food outside for the nervous. Tuna etc. inside the cage is the reward for the bold. When they get confident going in for the delicious, and they’re all in there together, gently close the trap. Also, draping a towel over the top of the cage will help you to close the trap without them getting alarmed by sudden arm movements. A bit depends on the type of trap, so practicing beforehand with the cage would be a good idea.

From the photos it seems they let you get pretty close, so sitting beside the trap might be a good way to be in position to close the door when a suitable opportunity arises. Unless the camera was zoomed I guess. The backpack so close to them is really good sign that they are not scared of your smell.

Then drape towel fully over the cage and transport them to the vet/refuge etc. Put thick towel over cardboard under the cage in the car in case they wee or stress poop through the base of the cage.

Be aware that you can catch almost any cat in almost any trap - ONCE. So you’ve got to get it right the first time as they won’t let you trap them twice.

If you miss one or two, you might be able to set the cage with tuna out again the following day so see if they’ll approach it. The smell of the rest of the family on the cage might actually help with this.