Other than Osborne House, what sights should we see on the Isle of Wight?
Definitely walk to the Needles, but don't go too near the cliff edge! A little scary!
You don’t say what your interests are, so a good starting point would be to look on the Trip Advisor “what to do in.....” section, rather than us suggesting things that don’t appeal.
The IOW has changed, but it used to be a bit like stepping back a few decades, as like everywhere, it used to be quieter, but it’s a charming place.
Have you not researched the island before booking your trip there?
I can't tell you what sights you should see because I don't know what interests you. If you're intending to visit Osborne House have you considered membership to English Heritage? I don't know your location but there is an overseas visitors pass that provides free entry to all English Heritage sites, you can buy a 9 day or a 16 day pass, a 9 day 2 adult pass costs £57, considering an adult entry fee to Osborne House is £17.20 you can see how quickly the savings mount up. You can visit Carisbrooke Castle, Appuldurcombe House, St Catherine's Oratory and Yarmouth Castle as well as a number of nearby sites on the mainland around Southampton and Portsmouth plus it also includes Stonehenge if that is on your list.
www.english-heritage.org.uk/visit/overseas-visitors/
The National Trust also offer an overseas pass, however there's not an option to collect the pass on the Isle of Wight for some reason, the closest place would be Mottisfont in Romsey which is a good enough reason to visit.
https://shop.nationaltrust.org.uk/gifts/exclusive-gifts/national-trust-touring-pass.html
The model village, down to the beach at Alum Chine, Blackgang Chine if you have children. There's a nice steam train too.