Hi
If you live in Spain you will not get free schooling in Gib for your children. When I looked at the costs last year I seem to recall that it was £3000 per term per child. The cost of International schools is even higher. Spanish state schooling would be free.
Not sure which schools are the best but if you did decide to commute into Gib you probably want one closer to the border. However, there are border queues from time to time so you would need to give yourself plenty of time.