if you bought an ori wii from australia, the only games you can play on your wii is from australia (which is PAL coded)

if you intend to buy a game from KL, you will need to buy an ori game that is PAL coded...and if you somehow got an NTSC game, it will not work although the game may be original (cos of different region and wii region locks itself)

well, as for the network connectivity...
i wonder how are you gonna burn yourself another copy of the original game, considering that if you have an original wii and don't have any soft modding skills yet i assume (cos burning wii games may be a lot more difficult than burning a PC game i suppose?)

if you somehow manage to burn a copy of the game...that will be known as a backup, and you will not be able to play backups without the homebrew channel...considering that you have an original wii...i doubt that you will have this channel...and if your system version is 4.2...(that is if you perform your system update regularly)...well, it will be more difficult to get the hbc installed in your wiis

what is the HomeBrewChannel(HBC)? the HBC is a channel which allows you to softmod your wii...and well, ninty don't like that channel much and 4.2 is regarded as the HBC killer as of time now...(where it erases the whole channel from your wii and will brick your wii if the update is done on a korean wii)

if you have all the above (or maybe you bought 2 of the same PAL games)...well, as long as you have your sis's friend code (and she also have a PAL system)...there will be no doubt that you can 100% connect to her

u didn't mention if your sis have an australian wii too. i assume not. by the book, u will need to purchase 2 copies of the game. softmodding is not advisable unless u acquired the skills and u r dedicated to go down that path.

btw, is good to know the games u intend to play. i remember reading somewhere that some games don't support inter region online multiplayer. i could be wrong, but i swear i read about it. but do mention the games and we can look up particularly to that game.