bringing family in Qatar is not just a joke...you have to consider a lot of things, children's school, wife's status in living with no one to talk to..lots of things. paperworks can be done as long as you have all the legal papers needed.
The minimum should be six months before they could join you since they will ask for your bank statement for at least six months, either it is government or private companies,it will all depend on you, how it will take you to provide the legal papers they need...