If you want to keep the family happy I would go for Windsor or Bray, all the best bits of the river and stuff to is above there. Penton is a good marina but that bit of the river has less to do and fewer places to stop. Remember the river is not about cruising between different marinas, you will miss everything the Thames has to offer. Make sure you can survive without shore power and you will love it.
Not sure what issues Whitelighter had but the marina is only somewhere to park, enjoy the rest of it you can take a lifetime and still not do it all.
There is a row going on about illegal development and breach of planning conditions somewhere around there. I would check carefully. Parking may well be an issue too... Hampton Court area gets very busy at times and the parking authorities can be very keen.