Hi David
You are brave to step into our parlour !
I'm not in here often so feel like a bit of an intruder too. I've been kicked off for trying to help people find information a few times so will attempt to help without breaching the regs.
suggest your sister or yourself if you feel like it does an internet search using terms like :
Lesbian Parents Australia
same sex families
lesbian families
lesbian conception
There are also groups on yahoo.
There is a wealth of information out there and your sister and her partner need to do some research so they can get a better picture of which way they might want to go about becoming parents and then they will start to have some specific questions to ask .
Best of luck