Do I have to fill in the passport profiles of all family members, select all, and then fill in the declaration form once, in the Mobile Passport App?

Question

So I was setting up the Mobile Passport App(for Us citizens and Canadians) for two of my relatives and it says you have to submit only one 'New Declaration' form for one family. There are two passengers, so do I have to fill in the passport information and make a profile for BOTH of them? And then they'll have to select both passport profiles when filling in the form, on arrival at their destination? Or do you need just one passport profile for the whole family? Since it says only one form is needed