Dear Creative:
The IMM 0008 generic is for immediate family members and principal applicant. The term "Immediate Family Members" consist of only spouse and children. Mother/Father/Siblings and other members of family should be filled "Additional Family member details section" which is IMM 5406 form.
Does it require you also fill out information of yourself? I'm single and I'm ready to fill out "N/A", but not sure if I should also fill out information of myself on page 2 of imm008 for "details of family members". Many thanks.