Q: itunes for multiple family members

My situation is I've been using iTunes since its inception and built quite a library. I've been through multiple ipods and now on to iphones for multiple family members. All the while using one itunes account on separate devices for multiple family members. Now that we have iphones its become necessary to create separate icloud accounts for each family member. This creates a problem for those with new icloud accounts. The iTunes music library can no longer be shared on separate devices (that I know of). The music library and playlists I have built over years cannot be shared with those devices that now have separate icloud accounts. I am aware of "family sharing" and have set that up going forward but how do I resolve the issue of all the music and playlists that were shared when we all used one itunes account, prior to creating separate icloud accounts? I hope this makes sense. For example my wife and son no longer have access to any of the music/playlists on their iphones that they used to have prior to creating their own accounts. Even though all purchases made before and after creating separate icloud accounts were made using the same credit card.

I believe I could just go back to having the other devices sign back into my itunes account and I think that may resolve the issue but what happens to purchases that were made on the other devices while they were signed into their own accounts? Another point that comes up is that we all have gift card balances on each itunes account. This is so confusing