Sale by father to one his sons

Whether it is self acquired property of grand father? if yes then no problem for your father. 
If all the properties are ancestral properties then everyone has got equal right over the property of grand father.

If grandfather is no more then your father can claim his share in the remaining buildings

Your father can claim his share from the remaining property of your grandfather if he dies intestate.

My doubt is whether any of uncles (my father's brother) can claim that the purchase of one building by father from my grandfather with the concert of my uncles (my father's brother) is void. ie purchase of part of undivided property is void. In other words, whether my father's brother can have right on the building purchased by father from my grandfather only because purchase event happened before division of property.

If the sale was valid and for consideration then your uncle cannot claim the property sold to your father.

you should provide with documents why your father in law has sold that property your father and show those documents to your uncles because no on will agree that already your grand father has property and why he sold that to your father who already will get share right from the ancestral property 

means your uncles may question the sale process why it has to be done 

If the peroperty  in question (4 buildings) are the self acquisition of ur GF then the uncles/ ur aunts cannot question the deal. U have also stated that the consent of ur uncles was obtained before the deal.As such ur uncles will be estopped from disputing the transaction subsequently. If on the other hand the property is ancestral property in the hands of ur GF, then all the memebrs of the family including ur fathers sisters also have equal rights in the property. U have not stated whether ur father has sisters, if so how many. If there are sisters, as their consent was not obtained for the deal, it is possible that the sisters mayraise claim for their share in the property including the one purchased by ur father.