Phytosaurs are basal, Aetosaurs are the sister-group of Crocodilians and the Rausuchia are paraphyletic. Most stay on their own branch but some, including Poposaurus group with Ornithosuchia.
By this, you mean Ornithosuchidae and not Avemetatarsalia, right?
The conclusion was that the tusks were probably not used for intra-species fighting or display, nor for defence, but that heterodontosaurs were omnivores living in semi-arid habitat and used the teeth to kill smallish prey.