For the community property adjustments, you determine the total amount, then do an addition or subtract adjustment so that you report the entire amount. For example-
Income A: $60000 B:$40000 TOTAL= $100,000 (one half=$50,000)
A subtracts $10,000 from $60,000 to equal $50,000
B adds $10,000 to $40,000 to equal $50,000