Are you coming alone in 3 weeks time or is your family coming too? If possible, it would be better if your children didn't arrive until the end of the summer holiday. They will become very bored after a summer in Doha. Better to leave them at home with their friends. Yes, the schools will be on holiday, but the office staff will still be there. As pwb78 says, the best school will be the one that will take them. Send some e-mails and visit the schools when you arrive.