IF they filed MFJ-together last year too, then the AGI is the same for both of them......line 8b of their 2019 form 1040.
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Exceptions: If they filed late in 2020 for 2019 on paper, or if their 2019 tax return is not processed yet...then that might be rejected...and you might have to set the AGI as zero for both of them....but you would probably wouldn't do that unless the first e-file attempt is rejected.
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*