My Mom died this summer and was receiving SS, so I am familiar with how it works regarding date of death and the one time death benefit. I don't know how survivor benefits work so I can't help you with that.
You're entitled to a SS payment if you live the entire month. Partial months do not count. So in athena53's case, she would be entitled to an SS payment for October but not November.
Payments are made one month in arrears, so the payment received in November is for October, and you get to keep that deposit and all of the deposits before that one. You are not entitled to any payments after that one. If SS paid you anything that you are not entitled to, they will claw it back. This did not happen in my Mom's case, so I don't know how it works exactly, but I believe if they do autodeposit via ACH (probably the most common situation), they will autowithdraw via ACH. Woe to you if the funds are not there for them to claw back.
My understanding is that the day of the month in which you receive the payment is irrelevant with respect to death. You received your November payment on whatever date you received it because that was the day your husband was assigned - probably based on his SSN or something. Regardless of what day you received it in November, it was your November payment for him living through the entire month of October.
My understanding is that you have to live the whole month in order to qualify for benefits for that month. So it wouldn't have mattered if your husband had died on November 2, November 15, or November 28, before or after receiving his November check. He would still not be entitled to that month's benefits and should not have received / is not entitled to a check in December.
You'll also receive a $255 death benefit. In my Mom's case, she died on June 6 and the $255 was deposited I believe on July 31. So I would expect you to receive your $255 payment on or about 12/31. IIRC this was a separate payment deposited on the same day.
I do not know why SS paid you a larger second amount ($1901). My only guess is that the second payment included his inflation adjustment, but I would expect that to happen in January, not December.
From what you've described, it sounds to me that they will eventually try to claw back the $1901. You should leave that money in that account so they can claw it back. I would also contact your local SS office and have them review it so that you can settle the situation sooner rather than later.
My condolences on your loss.