Yes, they are marsupials but not the only ones.
No. Numbats do not migrate. No native Australian marsupials migrate. Some species are semi-nomadic, but the numbat is not.
No. Only one or two species of Australian marsupials hibernate, and these are only those found in alpine areas.
Bilbies do not hibernate. Most Australian marsupials do not hibernate. Only the Mountain pygmy possum is known to hibernate.
Koalas rarely drink, but when they do, they drink only fresh water. No Australian marsupials can live on saltwater.
Bilbies do not hibernate. Only one or two species of Australian marsupials hibernate, and these are only those found in alpine areas. Bilbies live in desert araes, not the mountains.
The correct way to write the scientific name for the genus containing marsupials, including the opossum, is Didelphis. "Marsupials" is not part of the scientific name since it is a general term for a group of animals with a distinct reproductive system. So, the correct scientific name is Didelphis only.
The opossum is not the only living marsupial. It is, however, the only living marsupial in North America. There are hundreds of species and sub-species of marsupials on the Australian continent, and a few in New Guinea.
No, male marsupials do not have pouches. Only female marsupials have pouches to carry and nurse their young.
No, skunks are NOT marsupials. Opossums are the only marsupials in America.
No. Marsupials are mammals, so they have fur or hair. Only birds have feathers.
One cannot compare whether or not a particular animal species is "better" than another. Both of these native Australian marsupials are completely unique and suited to a particular niche. While the Tasmanian devil is Australia's largest remaining dasyurid, or carnivorous marsupial, the mountain Pygmy possum is the only Australian marsupial that hibernates.