First about Amar - we know him only from FBs of Megha and FIL. Amar seems to be very ideal son, brother and husband too. But he too went against his family and married megha facing opposition from both the families(Amar's & Megha's). Also he took up a job in Bhopal against his mother's wish. But still his parents understood his position and accepted him, i guess.
Now coming to mohan, here we really don't know much about his past. Mohan lives away from his family, apparently due to some issue of "principles" with his father. His father is rich but not a honest guy. We can infer this from Mohan's mom first scene itself. He is passionate about bringing the truth out through his work. There seems to be something more personal in this.
There is also some mystery woman "Rashmi" in Mohan's past - what happened there, we are yet to know.
From this i think mohan and amar share some basic qualities like honesty, truthfulness and integrity. The difference is that Amar was a very obvious good guy. But mohan has his quirks, cynicism (which maybe due to his past experiences) and his big enemy his "tongue". So noone will immediately understand his good qualities. Infact i think he didn't want others to know the softer side of him earlier.
From his seemingly careless, irresponsible behaviour, megha thinks he is childish and irresponsible guy, so she keeps advising him. She doesn't know much about him and has a very prejudiced opinions about him.