You don't have to send tax returns, they are just a suggestion. You can use utility bills, memberships, insurance policies, financial statements etc. Those in joint names are ideal but off you don't have that, individually named items to the same address would be another option.
So if I include the following does it look good for our proof of relationship?
- 2011 marriage certificate
- 2011 apartment lease agreement
- Warranty deed from 2012 purchase of house
- 2013-2016 tax returns
- Warranty deed from 2016 purchase of house
- 2 photos, one from wedding and one recent one
- messages from Dec 2nd - Jan 1st (starting point of being apart and day before i plan to apply)
I will also have a 4 months of bank statements with both our names on it but this is more for the financial side than the proof of relationship.