The decendants are the natural heirs. If they are not yet adults, the court will create a trust for their suppport. They will also appoint an executor to manage the estate.
The mother or father or legal guardian of the sisters. if there is no guardian the sister is next of kin.
If you are speaking of the relative or relatives entitled to share in your property if you die intestate (without a will) then if you are unmarried your parents are your next of kin. If they were deceased then your sister would be your next of kin. In another sense they are all your next of kin. See related question link.
Their parents or other family members would be their next of kin.
Mother, if you mean wife of the deceased husband.
If a man dies and is survived by his father and sister, the father would likely inherit the man's assets as a direct blood relative. In the absence of a will specifying otherwise, the father would typically be the primary heir according to intestate succession laws.
Her heirs would be her next of kin or whoever she names in any will.
Not necessarily. If the widower is unmarried, and has no children, but has parents or siblings that are still living - then they are the next of kin
In a case of no will, the next of kin has priority. Unless there is a will, the unmarried partner will not have any rights.
Generally, no. If the son predeceases his father and then his father dies, the heirs that are next in the line of descent of the father would be the grandchildren. However, the still-living father should have a will drafted so his property is distributed as he wants it to be.
If he has no spouse, yes.
Typically the state foster care system.
I would consult an attorney. If there is no will, you may have an entitlement to some of the proceeds. And if you are named in the will, you have rights to preserve the estate.