On your Two-Earners/Multiple Jobs Worksheet is line 1 less than line 2? If so, you should write zero on line 5 of the W-4 form, and you must also complete the rest of the worksheet (lines 4 through 9) to calculate an additional amount to be withheld. Then, yes, it means your withholding will be the amount for zero allowances plus the additional amount that you calculate and enter on line 6 of the W-4.
You don't write zero on W-4 line 5, or on line 3 of the worksheet, just because you are married filing jointly. You have to work through the worksheets to determine what to put on those lines. First do the Personal Allowances Worksheet. If the instructions at the bottom of that worksheet (below line H) tell you to use the Two-Earners/Multiple Jobs Worksheet, then you have follow the instructions for lines 1 through 3 on that worksheet to determine what to put on line 3.
Instead of using the worksheets, you might find it easier to use the Withholding Calculator on the IRS web site to figure out what to put on your W-4 form. The IRS Withholding Calculator is at the following link.
https://www.irs.gov/individuals/irs-withholding-calculator
