I agree with the other comments. They are a really tough plant. They are also very prone to spider mite - an occasional squirt of the foliage all over would help. A monthly application of very, very weak liquid fertiliser when watering would help along with a regular wetting agent. Weekly watering should be sufficient where you water until the water comes out the bottom. If more regular is required, then you need to repot.

I would contact a specific native retailer ie australianplantsonline.com.au that sells them and ask for their response. As Aussie Southern is a column shaped variety I wouldn’t expect it’s roots to be too wide roaming. But as it’s one of the new hybrids created for smaller spaces there may not be a lot of info on them.

They just need to establish themselves, if you teasesed out the roots from when you planted them that gets them going quicker, once they get going then they put on new growth, keep up the water , keep up the powerfeed, it took awhile for mine also but now they are huge and lush and are well over the fence, don’t give up on them.

I think by the look of the leaves they could have dried out, they like to be kept moist during the warm weather, you can cut them back, I have done this and they have regenerated again, but don’t let them dry out