The legal heirs of the deceased erstwhile owner should have executed a joint registered sale deed in favor of the buyer, hence you may verify the sale deed executed in favor of Krishna tht whether the property was sold to him by a joint a sale deed executed by all the legal heirs of deceased Chandra.
If the property was sold by the wife of Chandra alone despite having the legal heirship certificate, then the other legal heirs have to execute a ratification deed in favor of Krishna.
Second issue is about the name transfer of tax;
The property tax is on an unrelated person namely Charan, which has to be on the name of your vendor i.e., Krishna.
You can ask him to get the tax transferred to his name with the help of his vendors.
Let his vendors answer the problem and get the same clarified about the error in the name of the tax payer.
If Krishna is unwilling to change the name of tax payer to his name, then you may decide not to buy the property.
Did you obtain a proper legal opinion from a local lawyer, if not, firs obtain the same and proceed only if recommended.