Hi there ArthurBentgum,
If the settings you're choosing for changing your wife from an adult to a parent/guardian in your Family Sharing group aren't saving as expected, let's start by making sure your iPhone is updated to the latest software version, which is iOS 16.2. You can check that in Settings > General > About > Software Version. Learn more about updating your iPhone here if needed: Update your iPhone or iPad - Apple Support
Also, you'll want to be sure your iPhone is connected to a reliable Wi-Fi network with good signal strength. If this behavior persists, reaching out to Apple Support directly is the next best step. This link will help you get started: Contact - Official Apple Support
Take care.