Do the females hatch the eggs by sitting on them?
Yes. The eggs are quite large with thick shells. That along with the way the nests are constructed, prevents crushing under the weight of the mother.
Are you sure large eggs are practical? As the chicks then need a longer time to hatch and the warmer seasons of the year are quite short. Also the nest needs a lot of construction, and big animals need to feed a lot.
With respect to body size, larger animals have lower metabolisms and require proportionally less food than smaller animals. So it does not necessitate as much time for feeding. Breeding, construction of nests, and incubating will occur during colder months when the adults are actually living partially off of energy stores, perhaps fat (the winters are actually shorter as at this time the climate is significantly warmer globally). Much of the nest will consist of compacted mud and dirt, as well as vegetable matter.
Compared to body size they indeed need less food, yes. But as a whole a large animal does need more than a small animal. And I suppose they probably lay a small number or perhaps a single egg per season, in a fashion such as penguins? Also, do they nest in colonies or further apart?
Well actually as far as the incubation, perhaps it could work as it does with crocodiles and alligators. I am a little uncertain about it.
There's always the megapode method.
Or females could tuck the eggs under their wings rather than sitting on them.
I would say a single egg. And they would nest in clusters. Depends on the number of females in an individual male's harem.