Hi Lin,
Your 2nd Mary Brown is in Ford DZ 702 which is a public grave, so she is very unlikely to be with family members.
The 1st Mary Brown is in Ford K636, and is the only occupant.
However, the deed holder to H636 is Mary Brown, who is not interred within .
Other people in plot H636 are:
Robert Browne, died at Richmond St L1 age 64. interred on 25/1/1875
Honarah Brown died 5 Richmond St age 44 int 5/2/1885
Thomas Brown died 5 Richmond St L1 age 76. int 26/4/1887
hope this helps
Marienne