We submitted the following detail, we have submitted which all possible to show our relationship
- letter from our friend
- Tax letters of both showing the same address
- IC with the address
- Telephone bills
- photos, we submitted the photos which shows our long term relationship from college life(both studied at same college) to our child birthday photos with relatives, you may submit your travel photos too
- And the police report , which also shows the same address for both
- Bank letters
- Tenancy agreement
Submit everything which ever possible. One of my friend also had the same as your condition, they didn't have enough evidence to show that they have lived together for 12 months, and currently they are living together, so they provided all the evidence showing wedding photos, travelling photos, flight tickets and so on, and finally CO approved their application and they are flying to NZ by end of this month.
Submit the evidences which all you can collect before the timeline, if the CO needs more then again CO will ask you.
All the best