Q: How to use family sharing when already sharing the same iCloud account

My wife and I started separate iTunes account many years ago, and thus made many purchases on each account.  Some time later we started using iCloud, and when we did, we decided we wanted to share the same iCloud account so my wife, for example, could add entries in the Notes app and I'd be able to see them, and vise versa.  In addition, we have another iPhone for our daughter, and with that she has her own iCloud account in use on her phone, however, she is signed into my iTunes account on her phone (so her/my purchases were on the same iTunes account, namely mine).

Now, years later, Family Sharing came along and I'm trying to figure out how I can also make that work with the iTunes and iCloud setup we currently have.  My hope, with the Family Sharing feature, is that my wife's purchases (on her iTunes account) and my purchases on my iTunes account would be able to be shared.  That said, how should I go about setting up Family Sharing such