Partition Law and second wife son

My Grandfather(G1) and his brother(G2) has 3acres each, G2-My grandfathers brother didn't marry due which he thought give all his to My father(F1, i.e G1s son) and he did the same. Now My Grandfather(G1), and his son(F1) had equal property 3acres each. Then my grandfather(G1) made advantage of my father(F1) innocence and illiteracy, My grandfather sold that 6acres(3 acres + 3 acres) of land to someone else. Then with that money my grandfather brought 25 acres of land in some other place and registered the land on the name of my grandfather(G1) and my father(F1) and my babai(F2. ie my fathers brother). after 10- 15 years My grandfather(G1) invited a second lady into his life without permission of my grandmother(First wife). then a children(boy) born with this lady. after 13 years they have written a partition deed in that they have included that 12 years boy also, without the will of first wife sons. they have allotted major portion to that boy(second wife child) and my grandfather. My question is what are his(second wife son) rights on his partition deed? when my grandfather brought the land registered the on all the three i.e him, his sons through first wife, that means the first wife sons are the partners of that land/property right?