Buying a property or renting in Gib is very expensive compared to living in Spain.
However, the schools in Gib have a good reputation and the system is the same as the UK. If your kids are teenagers then this would probably be a good idea, otherwise you'd need to put them into an international school in Spain. If they are very young then the Spanish schools should be ok for your kids if they are already starting to learn the language before coming over.
With regards to Gib, some people love it whilst others hate it. You should maybe try it out for a bit to see what you think.
By the way, I am originally from Gib myself so I know the place very well...which is why I live in Spain!
Justin