basically he needs to report all of taxable income that he earns in any state to the IRS;unless he ia reg employee, I mean W2 employee, as an contractor, he needs to file Sch C of 1040 aslongas the amount on line 29 / 31 is $400 or exceeds $400 and also needs to pay self employment tax aslongas the amt on sch SE lline 2 / 3 is also $400 or exceeds $400. If he is filing as a sole proprietor, and/or a self-employed individual, your son should use Form 1040-ES, Estimated Tax for Individuals to figure and pay his estimated tax. However, he does not have to pay estimated tax for the current year if he had no tax liability for the prior year ;he were a U.S. citizen or resident for the whole year
;his prior tax year covered a 12 month period . if he ia a regulkar w2 employee then unless he earnes taxable extra income,i.e., capital gain , dividend income or etc, he does not needs to pay quarterly estimated taxes. Also basically he as a nonresident of those states ,needs to report any taxable income that he earns in each state to the state dept of revenue as a non resident of the state.but as you said, unless he earns any income from state resources, he does not need to file /report income to the states.