Do you mean two years of private for one child or for all three? Assuming your children are coming from an international school in Dubai, you could consider private for your Yr 10 child who will be starting GCSEs. In fact, many schools will have stated the course work already in Yr 9 but, particularly if your children are in the UK system abroad, I think it is perfectly possible to step in in Yr 10. RGS is very selective academically, do you think your child can pass the entrance exams? Other private options in the area for a boy are St George's or Reeds. Yr 10 is not a normal entry point, however, so you would have to call the schools individually to find out if they have space and how they assess for entry at that stage.
Both Philip Southcote and Freemantles are SN schools, Freemantles is for students with autism, so unless this is relevant to you, you can disregard them in terms of choice.
The best state secondary school in Woking is Saint John the Baptist but it is a Catholic school so unless you are Catholic your chance of getting a Yr10 place is very small. Winston Churchill is popular and ok-ish. Fulbrook catchment does not really extend to Woking, to my knowledge, so for attending there you need to live more towards West Byfleet, New Haw, Pyrford. It is large and also ok-ish. In fact, both schools are considered good by lots of people but bear no comparison to private options.
For primary, it is more difficult to advise without knowing exactly where you will live in Woking. The fact that you have mentioned schools from Guildford to Addlestone suggest that you haven't exactly narrowed down an area which matters much more for primary with their much smaller "catchment" areas.