Clause No. "12. The VENDORS undertake to indemnify the PURCHASERS against any loss, damages, consequent on proof of defective title as well as any loss, damages or expenses consequent or failure of scheduled property " is not properly worded, giving no meaning to last part.

Following  are the documents to be checked…

1. Original sale deed in favor of seller. (if sale deed is available, the risk of bank lean of property ruled out)
2. Original sale deeds of seller’s seller and linking documents.
3. Municipal records, as to whether property is mutated in seller’s name.
4. Clearance of municipal dues, electricity dues, water cess, telephone dues.
5. Whether the property self acquired by seller or ancestral.
6. Legal heirs/sharers in the property of seller for obtaining consent of all of them.
7. If property is newly constructed, the approved sanction plan.
8. A public notice to be issued seeking objections by unknowns to purchase of property.
9. Circle rate of property for payment of stamp duty.
10. Whether the plot is in green zone or yellow zone on in the Rajkalue region,

1. The clauses in the sale deed you have reproduced are the normal clauses to protect the Purchaser.

2.  To protect your interest as a Purchaser, get the legal opinion from a Lawyer regarding the title of the property, if it has not been done so far.

The said clauses are common. 

There's no illegality in the said clauses. 

However you may obtain a legal opinion from a local lawyer before venturing into the purchase of the property. 

It is sufficient to protect your interests 

however it is advisable to take 30 years title search 

obtain written opinion from lawyer that title is clear and marketable 

The clauses are sufficient. if you need more strength then use the following sentences

1. That the Vendor shall at all times hereafter at the cost and request of the Purchasers execute do or cause to be executed or done all such further acts, deeds assurances and things as may be necessary or expedient for the further and better assuring of title of the said property and vest the same with the purchasers.
2. That the Vendor further covenants and agree with the purchasers that the  Vendor  shall  at  all  times  hereafter indemnify and keep the purchasers indemnified against all claims, debts, damages losses interest costs and expenses incurred or sustained by the Purchasers by reason of any recital, averment, covenant, declaration or any of them in these presents contain proving or being found to be incorrect or incomplete or is not performed or observed by the Vendor or if any right privileges, or easements herein mentioned is obstructed by the Vendor any person claiming under the Vendor.

Dear sir/ma'am,

The contract of sale deed generally leans in favor of the Vendor. As it can be observed, that the man selling you the property has included the indemnification clause which protects you from any future loss that may occur as a result of wrong ownership of that land. However, you can renegotiate the terms and make the following changes to protect your interests strongly.

Elaborate the indemnity clause to include -

1.  A clause explicitly stating that all outstanding dues with respect to the said property have been cleared or will be cleared before the registration of the deed.
2. It can be further elaborated that it is free from any kinds of encumbrances like prior Sale, Gift, Mortgage, Will, Trust, Exchange, Lease, legal flaw, claims, prior Agreement to Sell,  Surety, Security, lien, court injunction, litigation, stay order, notices, charges, family or religious dispute, acquisition, attachment in the decree of any court, hypothecation, Income Tax or Wealth Tax attachment or any other registered or unregistered encumbrances whatsoever, and if it is ever proved otherwise then the money will be forfeited immediately. 
3. 
   Transfer of all deposits paid for electricity connection, water connection, taxes etc. can also be added to the agreement. The seller might ask for additional money if not included within in the sale deed.
4. It is also suggested that in case if you are not making the payment in installments, and you fear that the seller might back out before you complete the entire payment, you can include a clause that the Seller must return all the token amount paid in such a scenario along with interest depending on the delay of repayment.
5. That pending completion of the sale, the seller shall not enter into any agreement of sale in respect of the said property or any part thereof nor shall create any charges, mortgage, lien or any arrangement, in respect of the said property in any manner whatsoever.
6. Further, you should also hold the right to call off the sale deal before the execution of the deed, whenever you find a legal defect or in instances when you haven't received all the legal documents of the land or any other unforeseeable reasons
7. You can edit clause no.7, that deals with making repairs or changes to the property,  to make it more clear and specific. Instead of the term 'reasonably required' you may modify it to include any change that is 'fit for the purchase' or 'to the satisfaction of the purchaser'. This will ensure that any damage hidden or defect in the property will have to be fixed by the seller.
8. You may also include a penalty clause for any delay caused in handing over possession of the property to you as mentioned in the deed. This make the date of possession very clear and binding.
9. In case of any breach of agreement or if the seller has failed to comply with any terms, the money must be forfeited immediately.
10. Also make sure that along with the scheduled property all rights of easements are also transferred to you.

It is also suggested that you make sure that you have received all documents such as Katha certificate, Mother Deed etc. to be confirm the legality of the land.  Also ensure that the building is free from any claims of government possession.

Thank you.

These clauses have to be read with the actual description of the title history of the property

What if the title is infact defective?

What would you do with these clauses on paper after the seller has already been fully paid

I'd suggest you engage a competent lawyer to give an opinion on title of the seller to the property being sold 

It also depends what all due diligence you have done as a purchaser 

- These clauses are common in the drafting a Sale deed , to protect the interest of purchaser . 

- Out of this , you should take chain documents of said property , and mention the same in the sale deed. that the chains of the property documents already supplied by the vendor to the vendee. 

- Further, the sale deed must contain the clause , that the consideration amount has been received by the vendor before executing this deed. 

The above clauses are enough to protect your interest