If the donor did not have registered sale deed and the property was in his possession only o the basis of the sale agreement, then the transfer of property made by him in favor of his wife by executing a registered gift deed is not valid since he did not have marketable title to transfer the property to his wife.
If what I expressed is confirmed then the donee also is not having marketable title to the property hence she cannot execute a registered sale deed in your favor.
However you may refer the document before a local advocate and get his first hand opinion before venturing into the proposed purchase.
First of all obtain legal opinion about the genuineness of the property.
The bank formalities would be informed by the bank you may aproach.
If the property was transferred to the donee by the donor who had the marketable title to the property so transferred then this transfer can be held as legally valid thus you may look into other legal formalities, but if the donor did not have marketable title then the transfer itself is invalid, the bank may not grant loan even if you ignore the fact and purchase the property.