Must our separate income be reported as 50/50, or is there some written agreement we can attach stating that our income is not community property?
I don't know how separate works in community property states. But you know you might be paying more tax by filing separately? Joint is usually better.
How to file separate in Community Property states
https://ttlc.intuit.com/community/married/help/married-filing-separately-in-community-property-states/01/26030
Many people think they come out better when filing Married Filing Separate but they are probably doing it wrong. If one person itemizes deductions then the other one must itemize too, even if it's less than the standard deduction, even if it is ZERO!
And there are several credits you can't take when filing separately, like the
EITC Earned Income Tax Credit
Child Care Credit
Educational Deductions and Credits
And contributions to IRA and ROTH IRA are limited when you file MFS.
Also if you file Married Filing Separately up to 85`% of your Social Security becomes taxable right away even with zero other income.