Photos lost in iCloud due to turning off during backup
Apple can surely help you untangle your accounts. As a paying customer they will work with you to explain how to set up two separate accounts, then you can detach from one of the accounts - keep all the combined photos and then sync them to a new account. 

Once you have two iCloud accounts you can delete any cross contaminated photos that don’t belong to account A or account B and be happy again. 


http://support.apple.com 


This happens all the time when people wanted to share an App Store account for whatever reason and didn’t realize it might share more than you hoped. Hopefully it isn’t all your calendars / contacts / app settings that are mixed as well. That can take a couple hours to a couple days to sort out, but the process is the same. Get everyone their own Apple ID (and only one Apple ID) and then clean up once accounts are individual.