Three kids means that you will need to rent a three-bedroom apartment (as minimum), and those start from around 9000QR monthly, probably more.

You will also need to rent a car, a 4x4 SUV, which starts from 3500QR monthly, while internet + utility bills are average on 700QR per month, 250QR for gas "petrol", cell phone credit, around 250QR per month, and groceries could be anywhere from 3000QR to 5000QR depending on your lifestyle.

so you are basically looking at spending a minimum of 18,000QR a month if you want to lead a decent standard of living, so with school fees (average 6000QR monthly for American schools "for the 5 and the 8 yr olds") and say 4000QR for shopping, and nightlife, weekend trips ... 28,000QR ~ 30,000QR is good enough.

could probably settle for less (24,000QR) if you live on a budget.

I'm not sure about the good schools, but when you arrive, visit "Virgin Megastore" inside "Villaggio mall" near Aspire Park, and pickup your free copy of "Qatar Schools guide" ...

Good neighborhoods would be: "The Pearl", West Bay, Al-Dafna, Al-Sadd, Al-Nasr, Al-Mirqab Al-Jadeed, Aspire Zone (Al-Aziziyah, Al-Soudan, and Al-Ghanem Al-Jadeed) .. avoid the Old Airport area, Montazah, Mansoura, Nuija, Al-Thumama, Hilal, Najma, and Al-Wakra City

As for gyms, i would definitely recommend renting an apartment in a residential compound that has a gym and a pool, however, if it is not available, you can go to the gym and pool in the Aspire sports zone, for a membership fee of 300QR monthly

Hope this helped !