If you’re already a resident in Qatar and would like to get a member of your family for a visit, all you have to do is visit the Ministry of Interior website (click here) ; and then go to the MOI Forms section and download the “ENTRY VISA/EXTENSION APPLICATION” PDF and fill in the required information.
The visa is usually valid for 30 days, and can be extended by resubmitting the same form.
Requirements for applying visa for wife & Children:-
1) Filled up application form
2) Copy of personal ID or passport of the resident husband
3, Letter from husband employer citing profession and salary (Salary requirement is at least QR7000)
4) Copy of valid passport of  your visitor (family member)
5) Copy of attested marriage certificate & children birth certificate
6) Bank Statements (stamped) for minimum of 6 months (2 Copies)
7) Copy of attested work contract
8) Copy of house rental and kharamaa (rent agreement or company letter stating that housing is company-sponsored)

For attestation please contact sheen services as they are the best in Qatar who is very flexible, reliable with competitive price.http://sheenservices.com/contact-us.html