C. hillmanii is supposedly a coastal species that occurs on sandy soils. C. hillmanii is meant to have a diameter >20mm so your plants would be on the small side for the species. I believe this may be C. alata; which is associated with damp heath and woodland and has smaller flowers than C. hillmanii. C. alata apparently hybridises with C. carnea and it is possible these plants are hybrids, especially with the pinker flowers. Unfortunately I am not very familiar with either C. hillmanii or C. alata so I am hesitant to make a confirmation either way.
There were two clumps of these plants both of which were in damp heath, and there were carnea growing next to one of them so definately meets the conditions for an alata-carnea hybrid. And yeah, I've always thought of hillmanii and alata as coastal species but hillmanii has a pretty restricted range and habitat, much more than alata it so it would be suprising to get hillmanii there.
I asked Lachlan Copeland about this one and he reckons it’s just a regular C. alata. He also said that the “type form is actually pink like that” photographed plant.