Should I refrain from giving my father money, or should I help my husband buy a house or a piece of land, knowing that I have helped my father previously, and they constantly ask me for money despite my need, and my husband does not obligate me to spend my money?

If the parents are poor, their maintenance is obligatory upon their able children. However, if they are not poor, giving them money falls under the category of kindness (ihsan). If the questioner is in urgent need of purchasing land to build a house for herself and her family, there is no blame or sin upon her for spending her money for that purpose.