You do get to kill Janus later in the game.
You can use magic in the cellar of the building in the north west corner of the castle complex. Carry the chests there to be opened, or toss them out the front gate or over the wall. There are a couple keys around, as well.
Try standing behind NPCs and maybe use your sneak skill or a shadow potion before trying to Pickpocket. Tingalf can be pickpocketed with level 4 or 5.
Level 1 of Survivor's Instinct gives you 1 hit point every 12 seconds (1 time unit = 1 second). This can be handy to top off your health whenever you drop off loot or trade, but needs to be maxed for best effect.
