I have the exact same question. Is it:
One IMM5406 for One family? In other words 1 form filled by applicant with all the details of applicant's family and relatives for example's:
Applicant's Spouse
Applicant's Children
Applicant's Mother, Father, Sibblings
Which means Wife's Mother, Sister and Sibbling details would not be covered. However, if wife fills another copy of IMM5406 then it would be covered. But in that case there is no place to specify on the form that who is filling the form i.e. the Principal Applicant or Spouse of Children 18 years old. Which means how can you identify or notify whose Mother, Father and Sibblings are mentioned in the form???
From this I conclude 1 form filled by Prinicapl Applicant with details of his family and relatives. Please correct me if wrong.
Thanks