Does iCloud work iPhone to iPhone?

My iPhone is under the same account as my sister's. Will the photos, for example, that I take on my phone automatically transfer to hers as well? Just wondering.

ICloud works per account,

You'll each have your own separate account so if you log in using your account then everything that is backed up on your iCloud. So when you take photos with your iClouds account logged in your photos will Transfer to your iClouds account. While photos that she takes using Her iCloud account will transfer to her ICloud account.

As long as you keep your accounts separate and log out and log in each time then everything will stay separate