Hi Burhan, I applied with following documents and got family visit visa for my mother-in-law in 2 days time:

1) Application form filled
2) Copy of valid Qatar ID card of you and your wife
3) Copy of valid passport of you and your wife
4) Copy of valid Qatar Residence visa of you and your wife
5) Copy of your marriage certificate (in either English or Arabic)
6) Copy of your wife's birth certificate (in either English or Arabic) mentioning the name of your wife and your wife's mother
7) Copy of passport of mother-in-law
8) Original letter from your work sponsor citing your profession and salary

Your letter from sponsor should state your salary to be above QAR 5000 (I think so) and your profession should be a high-level one (engineer, doctor, accountant, manager, etc).

Best of Luck