I presume it is self acquired property of mother in law 

2) if so she can bequeath or transfer property by gift deed to her nephew and his wife 

3) nephew cannot be regarded as son of mother in law 

If it is her house then she is free to gift it to anyone during her lifetime. However, under DV Act you can file a complaint case under Section 12 of DV Act to seek injunction against the alienation of the house if it is shared household and such alienation will defeat your right to residence.

1. Wife has no share in the property of mother in law.

2. However in the event your mother in law die intestate then your daughter can inherit all her properties . 

3. Since property owned by woman is considered by her exclusive property she has every right to make bequest for the  same in her lifetime to anyone she chooses.

4. So if her nephew is misguiding her you can only make her aware about his ill motive. 

If the property is selfowned than she can gift it but it's ancestral or your father-in-law earned property than she can't gift it. Your husband share she has to keep away.

For time being by giving your daughter relationship ask her to gift property to your daughter or make the registered WILL.

1. NO. Mother-in-Law (MIL) CANNOT refuse you property since you & girl child are classified as Class-I Legal Heirs under the Hindu Succession Act and irrespective of anything, Class-I legal heirs have inherent rights over such property.

2.  Nephew & Wife, are classified as Class-II Legal Heirs under the Hindu Succession Act and they do not derive ANY right in property, as long as Class-I legal heirs are alive.

3. However to enforce Point no. 1 (above) and If there is a probable dispute THEN you would have to file Declaration Suit in the local Civil Court, with all relevant documentary evidences and seek appropriate relief and orders from Court. This can be done.

See if the property of your mother in law is self acquired then in that case the mother in law can transfer it to any person she wish. Though she cannot show nephew as biological son to transfer the property. 

Madam,

 you are the legal heir of your husband and she cannot directly transfer an property due to due in any of their favours. 

Depends on who purchased this property ?

If this is her self acquired property, than she can give it any. And if purchased by father in law than your son and you have claim in it. Your share cannot alienate by her.

1. In whose name the property in question stands?

2. If it stands in the name of your mother in law then she can deal with her said property in any way she feels like for which she won't have to show her nephew and his wife as her son and daughter in law.

3. If the property is in the name of your father in law, who died intestate, then you and your daughter will get a share in it.

if property is self acquired then she can gift or transfer to anyone. if property acquired by father in law then your daughter can claim her share. 

If the property belonged to yor father in law and he is reported to have died intestate then your husband (even if he is not living) is entitled to a legitimate share in the property as a right.

You and your child can claim your legitimate share in the share of your deceased husband and can file a partition suit if they do not agree for giving you your rightful share in the property.

You can also file an application seeking injunction restraining your mother in law from alienating or encumbering the property in any manner till the disposal of the main suit for partition.