Can father's 2nd wife claim share in his property?

The ancestral property was sold in 2008 by your father. You might have also asked to sign the papers along with your sisters. Ancestral property can't be sold without the consent of all the legal heirs.
Your father purchased a new plot in his name which means the papers are in his name The title deed of the property will be in his name only. Your name is mentioned as the owner after his death. As far as legal records are concerned this property will be his self-acquired property only. Even though you gave him money, that will not be there on the record.
A 7/12 Extract is a land record for tax collection purposes . It is useful to show as proof to show the possession rights of the land. The document is not proof of an established title. So based on 7/12 you can transfer the title from one name to another. It can not be considered proof of ownership. You can't claim your rights based on the 7/12 extract.
If your father married his second wife legally, she will also be eligible to claim as a legal heir to your father. She will have the right to claim her part in the property of your father unless otherwise, your father makes a will. Your father can give to anybody he likes by making a will before his death. You can not stop your stepmother from entering your property based on the 7/12 extract.
To get more reliable information about the legality of the 7/12 extract, it is better to consult a good advocate and show him all the information available and get his opinion.

Thanks Sir, But there is a query , my Name is on registered sale deed of 2008 as a 2nd purchaser and a co owner. The deed itself explains that the said plot was purchased jointly on our name and the name should be incorporated in 7/12. And can anybody challenge this sale deed after 14 years ? (Limitation ?). Can anybody throw me out of my property ?

As far as the acquisition of the property in the name of your step mother is concerned, no one can prevent her of her legal right if the marriage between your father and your step mother has taken place in the legal ways.She would be one of the beneficiaries of her shares in the equal proportions as other entitled members for the properties. Here it should be noted that in the the Hindu Communities, the properties cannot be deprived of their daughters in case of the parental deaths, though the sisters are not claiming any property rights.
It could be the entirety a different issue if your father has made a will of allocations of property based on 7/12 extract among selected members depriving your step mother.
To know more regarding the current issue, you might approach a reputed advocate to have further relevant inputs and proceed for actions according to his advice.

If you are sure that the purchase deed clearly states that you are a co-owner(co or joint buyer) and the property records at the village office show your name also as owner of the property, then thank God and try to save that 50%.

So as the first effort try to get precordial proof about the names of owners of land an bungalow. For this you have to get copies of all the deeds and deals made on the property since and including the purchase of the land by you and father. You can get this by applying for a non encumbrance certificate for a period from before your purchase, till date.

As the purchase of the land is made from the bank account of your father it will be taken as a fresh purchase and not ancestral property. But if you have to prove it is ancestral property it will be a very long and laborious process and may not bear fruits in any near period, as you have to establish that the purchase amount was sourced from the sale of ancestral property and y had also part sourced it. It is very very difficult, but not impossible, But there are more practical ways to safeguard your interest.

if the property and building is in your father's sole name then he can deal it in any way he wants.
So if you are afraid about it, then you have to approach court and apply for an injunction forbidding any further transactions in the property to protect your interest in the property. For this you need help of a vey knowledgeable and experienced good lawyer. But that can strain your relationships with father and others. So if you are god relations with your father, you may frankly discuss with him about your stake in the property and ensure that everything is honestly as per his initial promise and impression.

I feel that at least the bungalow( and even the whole land) is not in your name. Otherwise father could not have made gift deed favoring your sisters without your signature.

So immediately consult a good lawyer and if needed file for an injunction on the property and bungalow.

Your step mother will have right to claim (proportionately) the assets in the name of your father. You can have rights on the property specifically mentioned for you in the deed and other property records proving ownership. Your stepmother will have rights on the remaining property along with you.