For starters he is so hell bent of revenge that he some where seems to be going opposite of Raghu kaka. Agreed it might be Raghu kaka too has revenge in his mind just like Yug but he is waiting to get proof unlike Yug who is already on the path of revenge.
Yug already has started working on his plan. So what if he succeeds in bringing MJ down before Raghu gets a chance. I don;t think Raghu knows anything of Yug's plan and if they are indeed partners in crime should they not be aware of what they are doing.
Also if Yug was Raghu kaka's son how is that no one in the Shekhawat household is not familiar with him. They all knew radha so if he was indeed her brother he should be known .Unless he was a little boy at that time so no one figured out now he is grown.
On a different note where is Yug now. Yug is always in Nandu's house so how is that he was not around when Tara was sick. I understand that its because of the MriAra scenes but still .