Hi
Why you guys are into the thing of you applying first or him applying first..
Go For MUTUAL CONSENT. Now a days it takes hardly a month for Divorce Decree via mutual consent.
For the child if they give him to you its done..If they dnt then you can file a petition under Guardian and Wards Act for the custody.
Also if you are looking for future of your sis then leave the thing of teaching him lesson by paying something. As you said your family is well settled. Then leave the monetary matter and look forward for a better future.
Thank You