Messy Set Up - How to untangle Work Apple ID and Personal Apple ID and Family Sharing without loosing data

OK so we've made a bit of a mess. We are Apple fans and use MacBooks, iPads, iPhones and iMac's both personally (including our kids) and in our business. We have multiple devices old and new and 2 Apple ID's but there is a cross over and it seems like no privacy, everybody can see everybody else's text's, photo's etc. How do I fix this? Where do I start? How do I make sure I don't loose any data in the process?