The first three treasures you must get to finish Dragon's Lair 2 are found in the Castle while trying to escape the Mother-in-Law character. Sometimes the game will mirror scenes making all the directional options the opposite choice, so I can't guarantee if it will be a Left or a Right when you play the scenes yourself.
The first is an arrow, which will appear above Dirk the first time the snake appears, hit Up to grab it.
The second is the bow which will appear shortly after to Dirk's side, hit the appropriate directional to grab it.
The final is a key and will be hanging to Dirk's side while getting the fuel (?) for the time machine, again hit the appropriate directional.