*sultan is mohan n meera's son m not sure still...coz y mohan n meera separated is not clear yet! money cudnt have been the reason coz then MK wud have married radha and taken money and returned back to meera...so that's still a mystery ...
also, he gave his own kid to his driver assuming that his son will stay close to him and will be taken care of...but, rashid ditched him...
*now MK's suicide cannot be due to financial issues...
--coz he cud have sold sitaara studio or land where rk mansion is or the karjat farmhouse...
--radha's family was still rich enuf to help him once again
so its clear the reason for suicide is related to Rk ...i think the respect n faith Rk had in MK itself shattered MK which is y he committed suicide...his son was growing up and MK had started dreading about facing his son's hatred on knowing the truth and so he chose to end his life...
*now about the third point...Rk cannot be kuku's son..else, kuku wud have rubbed it in rk's head by now..but, there aren't chances of Rk being adopted either...coz then, radha wud have had the courage to push MK back to meera...but, she cudn't that proves Rk is her n Mk's son
So you are saying a misunderstand with Meera and Mohan happened he took his own kid and gave the driver to take care of him, his son will stay close to him, but Mohan stopped paying Rashid the money after a few months that's why Rashid abandoned Nazia and Sultan. If Mohan had carried on paying the money after that say until his death when RK was 12 years old he was still paying the money definitely Rashid would have stayed with his wife, why did he leave them because no money.
About the suicide you are saying it's RK's love for him and because he had a family somewhere else and didn't want to face RK's hatred over that. I'm not sure that was enough of an impetus for him to commit suicide, perhaps he did go searching for Meera saw she had gone mad and went searching for his son with her and found he was abducted seeing the state of his family (including Meera and Sultan here), RK's parentage the misunderstanding created in his mind by Kuku and his ruined business for a second time, he decided to end his life.
Your last point that Radha would push Mohn back to Meera, I don't think her character is like that, we've seen her behaviour so many times avoiding dealing with problems, she would never talk to tell her husband to leave.