I have to make some assumptions here:
1. The taxpayers filed jointly,
2. You were authorized to assist them in the past
3. you know the login name and password,
4. and you are their authorized personal representative or executor of their estate.
In that case, you can use the existing Turbotax online account to prepare their personal tax return for 2021. There is a checkbox for each person for "this person died during 2021" in their personal info section.
However, their income is only what was paid to them up to the date of their deaths. Income that was paid after death would be reported on a form 1041 Estate tax return (if the income is enough to trigger a return). To prepare a 1041, you need Turbotax Business, which is only available as a CD or download to install on your own PC, it is not available for Mac or online. Each estate would also need its own separate tax ID number. It is also possible that income paid to the estate of the spouse who died first passes to the second spouse, so that an estate tax return would only be required for income received after the second spouse died. This is an area where you might benefit from legal assistance.
If these persons are expecting a tax refund, you need to include form 1310. This is a form to get their refund deposited into your bank account, and requires that you provide proof, in the form of a letter from the court or other authorization, that you are their authorized representative. I believe you can e-file the return then mail form 1310 to the IRS separately. If not, you will have to print and mail the entire tax return instead of e-filing.
