You need the Alchemy skill to make potions. Alchemy Guide

The key should be straight into Lanilor's house, on the shelf with a plant and banner. Try hitting the alt key. If that doesn't help, you can get another key;
Lost Items - guide and directory of inventory files

If the exquisite wine bottle is not in Anthrabert's room, Corinna will accept regular wine as well.

Drag the skull into your inventory, then click on the chest.