That's a lot of tutors. Have you spoken to the school to see if they can give pointers or support? There is also a lot online which is free and just as good as a tutor. Not so sure about Spanish but take a look at mygcsescience.com, Hegartymaths and Mr Bruff for English, all extremely helpful. With GCSEs the best results come from doing as many past papers as possible and liaising with school to make sure you are covering the correct syllabus. I think nearly all schools also offer additional classes as well to support pupils at all ranges. Good luck. I say this with a DS doing his in the next few months and it is really worrying as you want them to do well, but they have to put the effort in which can be very frustrating, when you pop up to see how they are doing and they're on a mobile
have a look at the websites though and see if they can help before spending money on tutors.