U shlould do attestation of ur marriage certificate and birth certificate in Dubai External affair and Qatar embassy in dubai.Since ur marraige certificate and child birth certifiacte is issued in Dubai there will be no problem.After that go to the qatar embassy in the same area which is next to saudi emabssy and do the attestation, they will charge u around dhs 21/- per document.After that u can do the visa processing in qatar for ur family.