A: It depends. Did the six original owners take title as joint tenants with right of survivorship? If so, then the entire property belongs to the survivor. It would be surprising if that were the case, but not unheard of. You need to sit down with an attorney who can examine the title to the property so you know where you stand.
A: I expect the answer to your question lies within the language of the insurance policy itself. You would need to meet with an attorney and have him or her review the documents in question. If you are on good footing and the insurance company is in the wrong, then you will probably need to open an administration of the deceased beneficiary's estate through the probate court and have a qualified person appointed as administrator or executor in order to pursue the estate's claims against the insurance company.
A: If your mom left no Will, and the house is titled in her name, then it is inherited by her heirs. Her heirs would include her spouse if she was married at the time of her death, as well as her descendants. These are broad strokes. Exactly who receives what and in what proportion depends on more facts than I have available to me here. I suggest you take the most recently recorded deed to the property, your mother's death certificate, and meet with a local probate attorney who can advise you further.