The Story is getting interested day by day, Until today I was thinking that Sultan has backed from his promise which he made to Aladdin's Mother, the real reason was that, he forgot about the promise.
And it was Duty of Grand Vizier to remind the Sultan about the promise he made to the Poor women, the wife of poor tailor, But he was in greed of his son to be married to the Princess.
So, now Finally we know Vizier is the main Culprit behind all the happenings, As the marriage of his son and princess have broken, now he Should not do any other thing to be wall between Aladdin and Princess marriage.
As now the Sultan has recognized the Mother of Aladdin and remembered the promise he made to the mother of Aladdin, He should simply marry her daughter to the Aladdin,
But here Vizier bad intention come into play again and he asked the Sultan to demand the heavy dowry, from the Aladdin mother for the marriage of his son. Which he thinks will be impossible for the Aladdin to full fill.
I truly hate the concept of this Dowry, it's should be allowed in the society. We all know it is very easy for Aladdin to full fill all the demand of the Sultan with the Help of genie. But his mother was worried that how the Aladdin will fulfill these demands.