When I set up family sharing can we access each other’s text messages?

No. Everyone’s iCloud data is private, tied to their AppleID. You cannot share private data like emails, messages, contacts.

Family Sharing - Apple

Does it share all of my photos

It will share mostly Apple services stuff, like App store purchases, Apple Arcade, iCloud subscription, and Apple Music family subscription. Things that are personal to your device, like contacts, messages, emails, and photos (unless you chose to share it yourself) will never be shared to other members of your family. Everyone will still have their own respective Apple IDs