If you want to stay native as possible, you could try the following below. It may be a little janky and I'm not 100% sure if it'll work, but it seems like it should.
- Create a 3rd iCloud/Apple account.
- On each of your devices, go to Settings > Apps > Notes > Notes Accounts.
- Add this new account.
- Move the notes you want on both devices into this account.
Now you won't have to share them. They should stay in sync and be able to be locked.
Alternatively, if you don't care about having all your notes on your wife's phone (or vice versa), decide if you or your wife should be the "master" account for notes and add that account to the other phone.