1. See in flat co-owned by your father and his second wife you have 1/3 share in 50 percent share of your father , also in flat owned by second wife of your father she is absolute owner.

See your father paid amount and registered it in name of his second wife even though moment was received as inheritance father was absolute owner of it and he willing purchase flat on his wife's name so even you file suit she can contest and has strong ground. 

You can file a suit for same seeking that your father was owner of the property and he purchased from his own source of income second wife is just owner on paper.

Yes you need to file suit for cancellation of the sale deed before civil court

It is necessary to peruse sale deed mentioned b6 you 

2) sale deed cannot be cancelled 

3) you and your brother have to file suit to claim share in property bought in set mother name as bought for benefit of joint family 

If the flat is on your father 's name with jointly with his second wife, still you both are eligible for your share in the father's share.

You can apply for legal heirs certificate and succession certificate in the court and apply for mutations papers on your name.

At least ask you brother to make application for legal heirs Cert in the Tahsildar office and show every where you both also have rights in the property by applying as a legal heirs of your father in the property.

1.  Your query is phrased casually, hence difficult to understand and formulate an opinion.

2. Be that as it may, sale deed executed by your father in his wife's name cannot be declared void by the court unless you are able to prove that it was executed by him without free consent.

Your father in this case is not divorced so the property left after his death will be divided equally between all the legal hairs including his wife.

I will be difficult to prove that property in her name is purchased by her husband from the fund from grandfather title suit will take lot of time and energy and the feet of the title suit is not yet known.

Until and unless a person is divorced  the wife remain in  for her rights as widow and previous behaviour in not material.

Hi

File a case of fraud against her.

Also file a civil suit for cancellation of deed with all the proofs you have.

Thanks 

Sale deed cannot cancel, you can only file file partition suit. That lady has 1/3rd share in property and rest 2/3rd inherited by you and brother.

And you can continue the criminal case filed by father as legal representative.

1. You can file a declaratory suit praying for a declaration that the said flat actually belonged to your father since your step mother did not earn any thing and the consideration for buying the said flat was paid by your father only..

2. Once the Court declares that te said property standing in the name of your step mother belonged to your father only, then you and your brother can claim  share on the said property along with your step mother, being the legal heirs of your deceased father. 

There is no provision in the Transfer of Property Act or in the Registration Act, which deals with the cancellation of deed of sale. Registration Act confers no power with the Registrar to cancel a document which had validly been registered as per the Act and Without reviewing the relevant documents it is difficult to provide a definitive view

1. You can lodge FIR against her second wife for forgery of signatures of father as well as using fake documents for transfer of property owned by your father. 

2. You can also file suit to set aside the transfer deed on her name on ground of forged signatures, forgery of documents and fraud committed with your father. 

3. Only if you can prove above mentioned grounds then you can set aside the deed on name of your father's second wife. 

The property lying exclusively on the name of your father's  wife  shall be her own and absolute property.

Even though your father has funded for the property, the court will say that since he had intentionally bought the property on her name for her benefit, it becomes her own property hence there is no question of cancellation of sale deed or anything to claim the property by you or your brother.

Perhaps in the other property, you, your brother and his wife can have an equal share in his half share of the property which is on the joint names of both.

Yes you should file a suit for cancellation of the sale deed on grounds that the money paid by her belonged to your father and she didn't have any money.

Therefore you too have a share in it being his legal heir.