We really do want to help you sort this out, so let me substitute a few words to make sure we understand.
This is a dependent life policy, where she is the owner.
--This is a life insurance policy, providing life insurance coverage on the wife and a term rider (perhaps) for life insurance coverage for her husband. (We'll name her portion coverage A and the husband's rider as Coverage B.)
She had him on as a dependent spouse, (Coverage B) in which case the policy states she is the beneficiary of that part....He was the insured; she was the beneficiary (Coverage B).
--Main policy was on her (Coverage A). The intent was to have her as the beneficiary of the portion covering him (Coverage B).
I don't know what I am saying that is confusing....She named her only son as her beneficiary for her portion, which was the main part.
--She selected her only son as the beneficiary of her life portion (Coverage A) .
I guess you could say she was the owner and the beneficiary.
--She was the owner of the entire policy covering him and her. She is beneficiary of his portion (Coverage B)
The owner, my sister, is not the insured; her husband was the insured. He killed her, who was also the beneficiary of his portion of the policy.
--Your sister was beneficiary and her husband the insured of Coverage B)
It is called dependent life insurance when it comes to him.
--Again, an insurance rider onto her main coverage.
He killed himself after killing her. Who should get his portion of the policy? His estate or hers.
--First, her son still gets the proceeds of Coverage A. Your question is whose estate gets Coverage B proceeds. Here's where it will get interesting.
The insurance company will expect the coroner to determine if in fact her time of death preceded his. I know you're saying he killled himself after killing her, however, the actual time of death will best be determined by the coroner. I know this sounds really nitpicky, however, the coroner must determine if her death was instantaneous to his, or if she lingered any at all, even without any appearance of life.
The insurance company will also have to determine how to apply their suicide clause. Here's where one hour will make all the difference. If he died first, she immediately would receive the proceeds (on paper). If she died first, he would receive the proceeds (on paper), which would then pass on to his estate.
Hopefully her son would inherit some benefit from his estate as well, although there may be other heirs. With the mother's proceeds, however, the son does not have to divide with any one else.
I'm sorry for your terrible loss.