It appears that Elizabeth Jane and Emily were probably sisters:
CAPE, ELIZA J
Parents: WILLIAM T & JANE
Gideon LANG's obit in the newspaper does say that his wife Elizabeth was the eldest daughter of William Timothy CAPE, as does their marriage notice in 1854. Emily's marriage notice in 1875 says that she was the youngest daughter of W.T. CAPE of Sydney.
As was said earlier, you just need to do some research and follow the lines back.