Hello, I had some source books shared with me (Tasha's Cauldon of Everything is what is causing me grief right now), I have the free trial for the highest tier subscription, and the book's optional features aren't appearing as available in Character Builder, even though it says I own it every where else and I can read it. The Character builder is saying I have to purchase it in order to use the features, even though I know I own the book.

You don't own them if they're shared with you via content sharing, you have them shared with you in a specific campaign. Subscriptions don't provide content access. The content sharing is allowing you to read it, but you can only use the content in the specific campaign where the content sharing is turned on. Where is the 'everywhere else' that says you own it?

In the tab that says where all of my owned books are. and when I look up the book in any area of the site outside of character builder.

OK, assuming that you're talking about this page, under Current Product Licenses, for Tasha's, did you buy the whole thing (it'll say Sourcebook) as opposed to things like the class bundle or the compendium content? The only way the Optional Class Features will work in the character builder is if you bought the sourcebook option.