You will want to get a total for each category of income/deduction, then divide in half.
From the one half total, you will add or subtract to each person's share. For example-
A Income= $70,000 B Income= $40,000 TOTAL = $110,000 (one half = $55,000/each spouse reports one half)
A= $70,000 MINUS $15,000= $55,000 (subtraction adjustment of $15,000)
B=$40,000 PLUS $15000-= $55,000 (addition adjustment of $15,000)