Yes, what you really need to do depends on how complicated his return is and whether you need to import carryover items, or you can copy them over manually, or there are no carryover items. If you don't need to import, you can start from scratch--just make an account that is separate from your own. You do not need to file the return from the same account as the extension.
Also note that if your mother is still alive, then she will sign a joint return for 2023. Even if you prepare it, technically she "signs" it electronically. If you want to be able to deal with the IRS in all matters regarding your mother's taxes, she needs to sign over to you a copy of form 2848, which is a limited power of attorney for tax purposes.
https://www.irs.gov/forms-pubs/about-form-2848
And if your mother is not competent right now, and did not sign a POA in the past, then she can't sign one now, and you need to go to court to be appointed her and your father's representative.
