you can't efile any returns. first, efiling is closed for 2019 and prior years. second, the fact your kids have been claimed would prevent you from efiling in any case. online preparation is closed for 2019 and prior so you need to purchase either the CD (only if you have a cd drive on your computer) or purchase for download. note that it's too late to file 2016. the last date for filing was 10/15/2020.
https://turbotax.intuit.com/personal-taxes/past-years-products/
you'll need to file form 14039.
https://www.irs.gov/pub/irs-pdf/f14039.pdf
