Lilly pilly help

Firstly weed weed weed, then fertilise and watering

Yes a hard prune will do the trick. To thicken them up cut their height back by at least a third. And clear all those weeds. Also give them a good spray of Seasol (a plant tonic not a fertilizer) - all over leaves as well as at the base. Do this every couple of months. I'd also throw some dynamic lifter around the base too. You will probably need to cut them back this hard for a couple of years at least. Hopefully they will thicken up and look much happier. You can add some mulch between them too to help minimise weeds taking over again.

And congratulations on the new house!

To be clear, Seasol is not a cure all & should be used sparingly once a fortnight in a solution that looks like a very weak tea.

I would; Weed the beds thoroughly. Scratch back all the leaf litter & pop it in a tub then fill with water & soak for 2nights. Prune 30% of the trees back in small cuts & drop everything into the soil. Fertiliser like mushroom compost or chook poop lightly everywhere but in the dripline of the plants, cover with 20mm of garden soil, reintroduce the litter that's been soaking & water in well everyday for a week. When you can be sure there's no weeds coming back cover the ground with cardboard, again except the dripline & mulch with 30mm of tea tree or sugarcane mulch.

One week treat with white oil the other week feed. Should see great results by Christmas.

Fair bit of work but no reason you Can't have it looking as good as it did.

I would hand weed ,add compost,cardboard then mulch, buy the end of summer it should be looking good again.

I would be reluctant to prune too much off not because Lilly pilly can't take it mainly because you are trying to add privacy.

Also thicker garden edging will help keep the grass out I like to use logs.

Wow they look shithouse something is seriously wrong here, try as above but to me it look’s really bad for Lilly pillys to look like that almost like they are herbicide affected.