On grandfather demise your grandmother , your mother and 3 siblings have equal share in property 

1. If he passes away without the will then it will be divided as per the hindu succession act among all the legal heirs. 

2. Yes, this can be the case

3. Till he is alive he has the liberty to do whatever he wants with his property. 

Regards 

No precautions is needed.

This is a self acquird property of your grandfather.

All sons and daughters of your grandfather  from both first wife and second wife shall acquire equal right of inheritance to the said property.

Dear Sir,

Yes, your mother will get equal share in your grand fathers property.

After the death of your  grand father it naturally devolves on the following formula

Section 8 in The Hindu Succession Act, 1956

1. General rules of succession in the case of males.—The property of a male Hindu dying intestate shall devolve according to the provisions of this Chapter—

(a) firstly, upon the heirs, being the relatives specified in class I of the Schedule;

(b) secondly, if there is no heir of class I, then upon the heirs, being the relatives specified in class II of the Schedule;

(c) thirdly, if there is no heir of any of the two classes, then upon the agnates of the deceased; and

(d) lastly, if there is no agnate, then upon the cognates of the deceased.

Hindu Succession Act, 1956 [Section 8]

HEIRS IN CLASS I AND CLASS II

CLASS I

Son; daughter; widow; mother; son of a pre-deceased son; daughter of a pre-deceased son; son of a pre-deceased daughter; daughter of a pre-deceased daughter; widow of a pre-deceased son; son of a pre-deceased son of a pre-deceased son; daughter of a pre-deceased son of a pre-deceased son; widow of a pre-deceased son of a pre-deceased son.

CLASS II

1. Father.
2. (1) Son’s daughter’s son, (2) son’s daughter’s daughter, (3) brother, (4) sister.

III. (1) Daughter’s son’s son, (2) daughter’s son’s daughter, (3) daughter’s son, (4) daughter’s daughter’s daughter.

1. (1) Brother’s son, (2) sister’s son, (3) brother’s daughter, (4) sister’s daughter.
2. Father’s father; father’s mother.

VI.. Father’s widow; brother’s widow.

VII. Father’s brother; father’s sister.

VIII. Mother’s father; mother’s mother.

1. Mother’s brother; mother’s sister.

Explanation : In this Schedule, references to a brother or sister do not include references to a brother or sister by uterine blood

On his intestate death, his property will inherit by by 1/4th share each. And if great grand children is born, than share will be more less.

In his life time he can give his property to any one. Ask him to execute WILL and distribute share equally.

1. Money received from "legal" parents by said Grand Father (GF) will be classified as "self-acquired" at the hands of GF and CANNOT be said to be inherited /ancestral in any way. Atleast legally.

2. IF GF passes away without executing a WILL document, THEN "ALL" the residual legal heirs (without any exceptions) of GF would be entitled to EQUAL share of all properties of GF.

3.  Disputant or Claimants of GF, can stake claim by challenging the Will on grounds of insanity /forgery /coercion/ health grounds or any other imaginary dispute points (that would stand in court).

4. A dispute can be created by 1st wife's children, stating GF has promised half house to 1st wife and her children, by bringing on board 3-4 local witnesses and other documentary evidences. Though this would seem out of context, but this can be done, by a shrewd lawyer.

Keep Smiling .... Hemant Agarwal
VISIT:

All the children and wife if alive shall have equal share in the property of the Grand father if he dies intestate without will.

All the children of first wife , and second wife along with second wife shall have equal share in the property.

First wife children shall have equal share if grand father dies intrastate that is without will and they can file partition suit for same.

1) your grand father would not disclose contents of will 

2)you cannot know whether will has been made by grand father or not 

You can talk to his known lawyers about this. 

Check  in registry office if the will is registered. 

If still  doubt is there file partition suit just after demise  of your grandfather. 

File caveat in district court and high court in respect of probate of will. 

See will is kind of confidential agreement you won't be able to know same if you don't have copy or details of same.

They need to present the will if there is will. You can demand from them to produce the will if there is any will. 

The  living wife and the children of your grandfather's both the wives  would  be his  legal heirs after his lifetime.

If your grandfather is not making any arrangement for his properties during his lifetime then all his legal heirs shall be entitled to an equal share out of his entire properties.

You cannot come to know if there is a Will made and kept secretly especially if it is an unregistered Will.

However you can ask your grandfather to make another Will bequeathing all his properties equally among all his legal heirs, and this Will shall  supersede the previous Wills if any.

1. IF will was properly registered in the registrar office, THEN you can depute a agent to search and obtain a copy of the will from the registrar's office.

2. IF will is not registered THEN there is no way to get such will.

If grand father is denying than there will no WILL, and in his life time, he can make any number of WILLs. Last Will will prevail.

Legal heirs would be all children of your grandfather for that house as well. 

This complexity may arise if he transfer the ownership of property during his life time. 

You should ask your grandfather to make a will in favour of all children regarding his properties to avoid dispute after his death.