Lets look at how this works, except for those nationalities who avail visa on arrival the husband is sponsored by his employer and the family is sponsored by the employee .. so in most cases the employee needs to get his RP the apply for family visa...

Some employers get family on business or visit visas but then the family will need to exit Qatar and come back on employees family visa .. i.e. fly to Bahrain and come back

I personally feel that family coming later is better as the husband has a chance to sette into the job, get his RP and arrange proper accomodation to bring the family in..

There is no rule to it, my employer arranges family visa after the employee gets his RP

"The best way to predict the future is to create it".