What is the ruling on parents disposing of their son's money if he works abroad, and his parents are separated and each wants to build a house, and the son wants to get married? And is it more preferable for him to get married or to give them the money?

Yes, it is obligatory for a child to financially support their parents if the child is self-sufficient and the parents are in need. This falls under the command of showing kindness, as stated in the Almighty's words: "And your Lord has decreed that you worship none but Him and that you be dutiful to your parents." This obligatory financial support includes providing suitable housing for them.

If you are in need of money for marriage and it is not obligatory for you due to fear of temptation, then you have more right to the money than they do. However, giving them money is one of the greatest acts of devotion.

If your marriage is obligatory for you due to fear of temptation and unlawful acts, then saving for the future obligatory marriage takes precedence over their current financial support.

However, if you are not in need of money, then they have more right to it than you, as long as they are in need of it to the extent of their necessity.