If they could reach parts of Australia they could possibly do well, if they bring their knowledge of farming and horseback riding (alongside the required domesticates). Eastern Australia seems like a reach, but possibly reaching the areas around Perth could do well for them. Its relatively hospitable and arable, and they could farm and set up agrarian societies there. Its doubtful that they spread to the interior, even with horses though, due to how inhospitable it is. After some time and diffusion however, the Aboriginals could very easily adopt their farming techniques as well as possibly their animals, allowing for more permanent societies set up across Australia, especially the coastal regions. It seems likely the Indo-European group however would be locked in their corner as an isolated culture group, which would allow for some interesting cultural developments. The basis of their culture and religion would be Indian, but time and separation would make them completely unique.