Are the Twins (who aren't really twins) British?
 

Pretty sure I can hear a quasi British accent behind the shrieks.
I'm guessing their British but have lived in Australia for quite some time.

Their mother definitely is. When they were introducing them and they showed them at home she had a very strong English accent. I can't remember what type (area) accent it was off the top of my head though.
Maybe the family moved to Australia when the girls were young or maybe they were born over there and have just picked up some of their mother's accent.

They obviously saw Samanda and wanted to be them for Australia, weren't gonna let the fact they weren't twins stop them.