Thanks a lot for sharing the link, it was super helpful and I was able to successfully link the application.
Here are the options that I selected,
1. Family Name, Given Name and DOB
2. Passport details
3. For number of family members, I added 2, 1 for myself and 1 for my sponsor, this was a little weird as our total family size is 3 and this can be the confusion part. I think the idea is to include total number of people who will be processed in the application i.e. Principal Applicants, sponsor and co-sponsor (if applicable) and total number of dependents.