If the property was in your mother's name alone and she died intestate the property would pass according to the laws of intestacy in your state. The children may be entitled to a portion. You can check your state at the link below.
In the event the step father is deceased, yes. But, you will need a copy of the death certificate showing that he is in fact deceased. Also you will need to know if he had a will that willed the property to someone else.
Then someone else is and must follow the wishes of the deceased.
Yes. in many cases it is a requirement of law that the spouse gets a life interest in the property. The property probably became your father's without any need for an estate, as the survivor.
You need to go to a law library in your jurisdiction and read the law. It will tell you when it became effective.
You can only deal with property that you yourself own.
If all assets were held by the couple as joint property with the right of survivorship then full ownership of the property passed to the father's companion when he died. The children would be entitled only to property owned by their father in his own name alone. Any such property would pass to his children under the state laws of intestacy if he died without a will.
If the property was conveyed to a sister by deed from her father then she is the owner of the property regardless of whether the father is living or deceased. Deeds have no other "meaning" except to convey property to the grantee on the deed unless other intentions are clearly stated in the deed. Father should not convey the property to one child if he really wants all his children to share in the property. By executing a deed to one child he is telling the world his intention is to transfer ownership to her alone. If father is deceased, unless you have written proof that your father intended that your sister was to hold the property in trust for all his children then you are out of luck. The grantee on a deed is the owner of the property unless there is written evidence convincing enough to persuade a judge to rule that others have an interest in the property.
If their father is deceased, all of his children have some rights to his estate, unless specifically denied them in the will.
Yes. Under Hindu Marriage Succession Act, all children married or unmarried have a right to the property of a deceased person.
I don't know what country you're talking about but there is no such law in the US. When a person dies, his or her property will be left to whomever is named to receive the property in the will. if there is no will, the property will go to the spouse. If there is no spouse, the property will be inherited equally by all children of the deceased. If there are no children, no spouse, and no will, then I'm not sure.
Yes, just as mothers do.
No. Generally, heirs-at-law must be related by blood or by legal adoption. Your father's second wife is not related to his children by his first wife. If the children were legally adopted by the second wife then the answer is maybe, depending on the laws of intestacy and whether she had a will leaving her property to someone else. You can check the laws of intestacy for your state at the related question link below.