1. Ask first son to issue GPA to his relative in India. GPA has to attested by Indian Consulate in U.S.A.
2. GPA holder should sign the sale deed as assenting witness.
3. Legally sale proceeds should be shared equally between son in India and son U.S.A. But as both are signing it is their problem. You will not have any problem on that count.

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.

If there is no will then succession certificate is a good thing to check before buying 

Otherwise take a noc from all the legal heirs on the sale deed itself as confirming parties. 

1. You may have to obtain the documents and present it before another lawyer and obtain legal opinion  and proceed only if recommended. 

2.  From your contents it can be seen that the property devolves equally between the two sons hence there is no question of splitting the sale consideration amount to the proportion as suggested by the lawyer. 

The grandson, i.e., the son of one of the sons of the deceased owner is not entitled to any share in the property, at least not during the lifetime of his father, hence you do not have to agree for the suggestion to split the sale consideration amount made by the lawyer.

If at all the sellers want the amount to be split in the manner as what the lawyer suggests, you may better obtain an agreement or NOC from both the sellers to this effect duly notarised and proceed with the payment as requested by both the sellers jointly. 

Grand son has no share in property 

2) sale proceeds have to be split among sons equally 

3) check whether original documents of title are with seller 

1.  Obtain Photo ID of both the Sons, such as Aadhar Card, Passport, Pan Card, Election ID Card, etc.

2.  Also obtain certified Family Tree.

3.  When a Hindu Male dies intestate, the deceased person's property devolves equally to his mother ( if alive ), wife, sons and daughters. In the instant case wife and unmarried daughter have also expired and only two sons are alive, then the share in the property gets divided into two sons in the ratio of 50% each.

4.  In the instant case, Grand Son has no right over the property. However if the unmarried son consents for a higher share to his brother or agrees for splitting the share into three equal half, then let the unmarried son execute a registered Release Deed relinquishing his partial share in favour of his brother or nephew, as the case may be, and retaining his agreed share.

- As per law , after the death of the owner , his property would be devolved upon all his legal heirs equally 

- Further , if any of the legal heir is died then his share respective share can be claimed by his legal heirs 

- Further, in the absence of a released deed from the legal heirs , the right of claim will be intact there. 

1. The consent of the son residing abroad and mother is required legally 

2. Since the first son is alive , then his son cannot claim any right over the property and he is having his right to sell his share in the property

On demise of original owner his wife and 2 sons , one daughter had one fourth share in property 

2) on demise of daughter her one fourth  share devolved on mother 

3) on mother demise her share devolved on 2 sons only 

4) both sons would have equal share in sale proceeds 

1. The daughter since died but unmarried, hence her share in the property shall automatically devolve on the other shareholders if she is not survived by legal heirs or successors in interest. 

2. You do not have to accept their demand to split the amount into 65 : 35 proportion, you are a buyer and it is your duty to pay the sale consideration amount to the sellers equally.

You may have to deducted tax at source accordingly from both the sellers out of the sale consideration amount that is required to be paid.

3.  You must understand that this not ancestral property hence the grandchildren are not entitled to any share inn the proeprty, therefore the property devolves only on the two sons, they only have to execute the registered sale deed in favor the buyer jointly, hence the sale consideration amount should be settled to both of them in equal proportion. 

- Since the daughter was unmarried , then after her demise her share will go to the survived legal heirs equally i.e. other two sons.

- You should pay the consideration amount to the two transferor equally only , and the said ratio payment can give your trouble in future. 

- Further , as I mentioned above that during the life time of the two sons , grandson having no right to claim over the property and the consideration amount legally. 

It's better to go for succession certificate