Do you know if getting multiple notarized declarations from friends and family would help? If so, we could prove multiple years of cohabitation for sure!
No, because that doesn't prove
you lived at the same address - a declaration from family and friends only appears on the checklist as proof of relationship, not cohabitation.
For clarity, to prove a common-law relationship, you
must prove:
1. that you have shared the same home for 12 months
(you need proof like bills, rent receipts, mail, etc. - considerably more than just one source)
2. support each other financially and emotionally
(you need proof of a significant degree of attachment, such as insurance, benefits, finanical support, gifts, letters about the relationship history written by each other, etc.)
3. have children, if applicable
(no explanation needed - this isn't determinative on its own, don't get pregnant just to immigrate)
4. present yourselves in public as a couple
(letters from family, friends, social media posts, marriage announcements, photos of you as a couple)
Declarations from friends and family only support point 4 unless they were your landlord. Even then, you need multiple points of proof for each category.