How can he prove he is jobless

Get evidences like his payslip or IT returns to proove same.

If not you bring relatives who did marriage and at that time what they told about guy's salary and company.

If above two doesn't work, file Crpc 91 and ask employer to provide details.

This guy looks like my wife's brothe....Not sure.

1.    Donot use Upper Caps while writing in a Forum. It points to you shouting at professionals here for no fault of there’s.

2.    He can prove his unemployment by filing an affidavit stating under Oath same and volunteering himself to Court Commissioner inquiry.

3.    He can prove his unemployment by producing true typed certified copies of ‘job rejection Letter’ from various would be employers and volunteering signatory as his side of witness for your side to examine them.

4.    He can prove his unemployment by filing signed / stamped ‘0’ IT return.

5.    He can prove his unemployment by filing true typed signed copy of 'job termination Letter' from his previous employer and volunteering signatory as his side of witness for examination.

6.   He can prove his unemployment by producing true typed certified copy of ‘Regional Employment Exchange Registration Letter’ and volunteering signatory as his side of witness for your side to examine them.

6.1 He can prove his unemployment by stating on Oath ‘mental cruelties’ your sister did upon him due to which he is not in right mental frame to get gainful employment. For this statement he will offer himslef as witness for your sister's side to exmaine him at the Box.  

7.    To para 2-6 your sister’s side’s counter is to subject his witness examinations and drawing inference of his capacity to earn based on minimum wage act that is all.