For the ancient shadow quest you need to get "something" to open up the barrier (can't remember what). The quest has several parts spread out all over Rithvale, check the map if you have some other flags that you can do.

Can't really help with the Carleigh's tower one. I have just beaten the game and replaying it now but only in act 2 still, can't remember what that quest was about. As a general advise, check the map for quest markers, the game is pretty good about marking where you are meant to go. And don't forget about TAB to highlight interactable items.

Got past the floating books and was able to complete the game. Never was able to get past the purple wall. Good tip on the tab!