1. See firstly the judgement you are referring of suraj lamps it is about that GPA cannot be instrument of sale means by Making a GPA property cannot be sold it has to be sold through registered sale deed. Though A GPA can be given to register sale deed that is valid. So the GPA in blood relative is valid brother using GPA can make a sale deed in your favour.

2 .If sale rights are there in GPA then Special power of attorney is not required if not then ask for SPOA.

3. No he received property from mother son of A has no share in the property.

1) elder brother son has noshsre in property as it is not ancestral property 

2) specific POA has to be executed by C authorising his brother B to sell the property 

3) POA should be attested before Indian consulate 

4) among blood relations GPA for sale of property can be executed 

1. The GPA is a valid one. 
2. As A has already disposed off his interests to B and C, A's son has no lawful interests from A. 

Purchase of property through GPA is valid if GPA is duly registered and stamped.

it is mandatorily required to be attested by the Indian Consulate.

1. A only had 1/2 undivided share in the flat

2. The GPA transfer by mother to A for her half share whereby A became absolute owner, is illegal as no transfer of property can happen through a GPA

3. Thus A could make a gift deed only for his original half share in flat to his two brothers 

4. The mother continued to remain owner of the flat for her half share. Technically her half share could have been transferred to A only through a registered release deed or under a registered gift deed if there was no consideration

5. As mother has passed away, her half share in flat will go to her legal heirs. So they need to obtain letter of administration from court and transfer her half share under a registered transfer deed to B and C

6. Only then can B and C be said to have clear title in respect of the full flat

7. PoA given by C to B has to be registered. The procedure which they have followed is correct. Just check that the GPA must be registered

8. You do not need to check the divorce papers of A as it has got nothing to do with the flat sale.

9. It is advisable to make A a confirming party in your sale deed

10. As long as A is living, his son has no right in his father's property 

If gift deed is executed without the NOC of legal heirs it can be challenged. But if it is a proper gift deed considering all legal heirs then there is no issue.

1. that is right no sale proceed can take place on the basis of the GPA, he will have to come to India

2. elder brother can now not claim the share in the property, since he himself has relinquished his share in the said property. 

Regards 

1.  The property shareholder B can very well sell the proeprty on behalf of his shareholder C on the basis of the GPA deed executed by him in his favor provided that GPA is registered in India after attested by the Indian embassy at Germany. There is no illegality in it.

2. Why do you want SPOA when the things are very clear and sufficient for sale of property. Dont make simple things complicated.

3. Elder brother himself has no rights in the property once he alienated the same by a registered document, then there is no question of his son claim any share in it as a right.

1. As per the information mentioned in the present query, makes it clear that now this fresh transaction would be based on the GPA.
2. As per the recent SC rulings, the property transaction by way of GPA or SPA or POA would not have the legal sanctity.
3. But, his is subject to the execution of the same in blood relation, so it can be done in your case, don’t worry about that.
4. But, yes, without release deed by mother for her share in the favour of elder son, would not entitle the elder to son to treat the property as his own on the basis of the GPA in 2011 and gift to remaining brothers.
5. Now, that gift deed as well as the GPA prior in 2011 would not have any sanctity if anyone out of the brothers object to it in future.
6. Rest, it involves more detail discussion as everything may not be possible to write in answer.