If your parents would be married filing jointly, and their gross income is greater than $23,300 then they would need to file a tax return.  

The IRS definition in this situation of gross income is below.  Social Security benefits are generally not included unless 1/2 of their benefits plus their other gross income and tax-exempt interest income is greater than $32,000.

If you have entered everything into TurboTax and it is telling you that their gross income is less than $23,300 then you would not need to file a return just to report dividends.

" Gross income means all income you receive in the form of money, goods, property, and services that isn't exempt from tax, including any income from sources outside the United States or from the sale of your main home (even if you can exclude part or all of it). Don't include any social security benefits unless (a) you're married filing a separate return and you lived with your spouse at any time during 2017 or (b) one-half of your social security benefits plus your other gross income and any tax-exempt interest is more than $25,000 ($32,000 if married filing jointly). If (a) or (b) applies, see the Form 1040 instructions to figure the taxable part of social security benefits you must include in gross income."  Page 2 https://www.irs.gov/pub/irs-pdf/p501.pdf