I would agree. It is probably a Saw-shelled Turtle (Wollumbinia latisternum). They have, in fact, changed the genus name again but most sources will not have the latest change. DERM still list it as Elseya latisternum.
Like many wild caught reptiles, it can be survive in captivity, including indors, if its needs are met. Due to the volume of water required to maintain acceptable water quality, turtles in excess of 15 cm straight carapace length are recommended to be kept outdoors in ponds. As Kitah pointed out, it is in fact being held illegally. You cannot actually keep it legally. So if your folks move, the thing to do would be to release it back near where it originally came from.
Richoman,
It sure ain't no "penny turtle" anymore! Or don't you know how big a penny is?
Ally,
The term "Penny Turtle" was applied to newly hatched turtles for sale, mainly in the 70's in Sydney. Hatchlings of Mary River, Saw-shelled, Southern Snapping and Eastern Long-necked Turtles were all sold under that title. They certainly did not stay penny sized for long.
Blue