1. Do I need to prepare separate Drafts for fees per application or one demand Draft for all three applications would be sufficient for OCI?
One demand draft for all three.
2. Does my family members need to be there with me at the BLS office? They have signed (thumb impression for 1.5 yr old daughter) the application.
No need for all family member to go. You can go there alone with all three applications.
3. We do not have our names entered as Spouses in our Indian Passports. DO we still need the declaration notarized here along with the marriage certificate issued by the Marriage Registrar at District Level in India?
I think you will need a notarized copy of marriage certificate, attested by public notary with photographs of both of you on it. Please confirm this from BLS office as I have heard that sometimes they accept non-notarized copy also. I would suggest you personally go to BLS office and ask them as call center agents are useless. They will give conflicting answers.
4. In Indian Passport, I have Given Name as "Harpreet Singh" and Surname is Blank. But, as per Canadian passport, the Surname is Harpreet Singh and Given Name as XXX as in Canada, we must have Surname. Technically, this is not a name change and I do not have to provide all the documentation related to the name change as there isn't any.
This is absolutely fine. They will print the name as per Canadian passport. My wife also had the same issue.
One suggestion, if you live in Brampton or Mississauga, do not use the courier service, prefer to pick up by yourself from BLS office. They will forcibly add courier charges, which will be around $182. As soon as you go to the counter, tell them first thing that you don't want courier service and you will pick up by yourself.