To answer your question - No, you do not answer "Self" when you did not have HDHP coverage, you answer None.
Family and Self refer to the type of HDHP policy that you had. A Self policy is just you, and a Family policy is you and any other person, even one not eligible to contribute to an HSA.
First question: what type of HDHP policy did your husband have from January to July. It was an HDHP policy, but did it cover anyone besides himself?
Second question: What type of HDHP policy did you have for September through December, Family or Self?
Third, yes, your husband can retroactively create an HSA for 2019 and fund it so long as you do it before April 15th(see footnote***). However, the amount he can contribute depends on your answers to my questions.
Fourth, how much you can add to your HSA depends on (1) your answers above, and (2) how much you (and any one else, like spouses or employers) have already contributed to your HSA.
I look forward to your replies.
***As of this edit, the IRS has announced that the filing date has been moved to July 15th, but has not updated the myriad of rules to clarify that this includes any regulations that depend on the due date of the return. So while the IRS will probably not mind you contributing to your HSA until July 15th, there is no guarantee that your HSA custodian - lacking written instructions from the IRS - will accept such a contribution after April 15th. In these uncertain times, it would seem prudent to make such a contribution by April 15th in any case.
[Edited 3/24/2020 2:13 pm CDT - updated for July 15th]
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