No.
Mississippi requires both spouses to file, even if one has no income, when filing separately. The exemptions are all halved. There is only tax on Mississippi income.
Missouri is more complicated. For him, he is a nonresident without Missouri Income. For her, she is a part-year resident.
This would be filed jointly with the income reported from other states backed off the return and/or a percentage applied to eliminate any non-Missouri income being taxed in Missouri.
For Illinois, he could file separately.
Mississippi: page 5: Separate returns (two returns) are filed when each spouse completes his/her own return. Each spouse reports his/her own income and deductions on a separate return. BOTH spouses must file returns even though one spouse may have little or no income. If one spouse elects to itemize deductions, both must itemize. Each spouse is entitled to only one-half of the total exemption authorized. Each spouse must list the other spouse on his/herreturn.
Missouri: page 3: Who must file: You do not have to file a Missouri return if you are not required to file a federal return. If you are required to file a federal return, you may not have to file a Missouri return if you:
a. are a resident and have less than $1,200 of Missouri adjusted gross income;
b. are a nonresident with less than $600 of Missouri income; or
c. have Missouri adjusted gross income less than the amount of your standard deduction for your filing status.
page 4: Nonresident: A nonresident is an individual who does not meet the definition of resident. If required to file, nonresidents with income from another state must use the Missouri Income Percentage (Form MO-NRI) to determine income percentages.
page 5: Other state income: You must begin Form MO-1040 with your total federal adjusted gross income, as reported on your federal return. Lines 1 through 27 of the return are computed as if you are a full-year resident. Tax (Line 26) is computed on all your income, and may then be reduced by a resident credit (Line 27), or by a Missouri income percentage (Line 28). The result is a prorated Missouri tax liability (Line 27) based only on the income earned in Missouri. See page 9, Lines 27 and 28.
page 6: Filing Status: Select the same filing status on your Missouri return as claimed on the federal return. If on your federal return you selected the checkbox “Someone can claim you as a dependent,” you will select “claimed as a dependent” on the Form MO-1040.
Illinois: page 4: If you filed a joint federal return and one spouse is an Illinois resident while the other spouse is a nonresident or a part-year resident, you may file separate Illinois returns. If you file a joint Illinois return, you will both be taxed as residents.
For Mississippi: 2019 Mississippi Resident, Non-Resident and Part-Year Resident Income Tax Instructions
For Missouri: 2019 Form MO-1040 Individual Income Tax Long Form
For Illinois: 2019 Form IL-1040 Instructions
