Give an accurate a retirement date as possible. No worry about the name change.
However, if your mother has enough income to qualify on her own to sponsor you, it is best practice for her to use the I-864 and be a joint sponsor, instead of combining her income with yours as a household member. When she does that, her husband should provide an I-864a. This is not just a "form" showing financial qualifications. It's primarily a contract between the sponsor and the US Government. When a married couple files a joint tax return, they expect both to sign the contract. You'll provide your own affidavit of support as the primary sponsor, no matter what your income of financial situation is.