Hi Realise this is an old thread, so hope you still read it!
Both Trinity and Valley Road are excellent schools, and very well regarded locally - many people choose them over private schools. If you like a very friendly, family atmosphere, you might also like to look at some of the schools in nearby villages eg Kidmore End (outstanding ofsted) and Sonning Common (not such a great Ofsted, but fab facilities).
The local secondary school (11-16) is Gillotts. Several friends have children there who are extremely happy and learning well. One thing to be aware of - and i will leave you to draw your own conclusions - is that many people who live in the Henley area send their children to private school, certainly at secondary level, even if this means financial hardship. It's quite an aspirational area! If your girls are super bright, there is also a grammar school in Reading, Kendricks. It's always heavily over-subscribed, but you are well within the catchment area in Henley.