Two questions in the additional family info section:
1. Is it ok if keep the country of residence and city of residence blank for a deceased person? Or should I mention where he/ she used to live.
If it is a mandatory field, enter the last place of residence. If it is not a mandatory field, I believe you can leave it empty or write N/A.
2. In this section I would only mention the family members who are not included in the application, right? Or should I mention my spouse and kid in this section as well, though they are included in the application?
Your family members other than yourself, your spouse and kids.
3. In the travel history section, what do they mean by family members here "applicant, if applicable, applicant's family members taken any trips outside their country of residence"? If spouse & applicant have different sections to inform about travel, who are these family members?
AFAIk, you need to fill travel details for yourself, your spouse and dependents. You don't have to fill it for other family members.