Q. Is there a max amount they can both get before it is taxable?
A. Yes. Theoretically, if they were both getting the maximum amount (currently $3113/Month*) or near the maximum amount, they would need to file a tax return, even if they had no other income
Social security (including SSDI) only becomes taxable when your total income, including 1/2 your social security, reaches $32,000 (Married Filing Jointly(MFJ)). So, a couple receiving more than $64,000 of SS annually ($5333/Mo), would meet that threshold.
So, for most people, Social security only becomes taxable when added to sufficient other income. If you are otherwise required to file a tax return, you do need to enter it in TurboTax (TT). TT will determine the taxable portion.
*$3895 for someone who waits for age 70 to start receiving SS
