HELP NEEDED!! PLEASE TRY! (:

Help me name a movie.
It's about 2 sisters whose mum died. Their father is teaching in a school. One night, a troll (or some mysterious creature) comes to their house and lead them into a ship. I think that there's a mermaid on the deck. And, there, the older sister gets the prettiest stuff and the younger one looks like a peasant. And, in a land, they get some assigments. I remember going to the half bull half man thing. And medusa. And "what is this? in the morning it walks by 4 feet, in the noon by 2, and in the evening by 3?" thing happens. And once they are in a land...meeting a unicorn, and they gave him a golden apple. I remember them wearing prettiest white dresses. And, in the end, they are fighting the bad trolls. and I remember they had to walk over hot things (the trolls). In the completely ending, they are back home and they were all like "OH! What a dream I had!"...so the younger one finds a necklace that was given to her by her mothers ghost. :DD

thank youuu!