Because the house is bought after marriage, the half of the son-in-law is the property of the younger daughter and son-in-law. In the event of divorce, the husband and wife are divided equally (each has half of the property, that is, a quarter).
The father-in-law's half also belongs to his husband and wife. If one party dies, the property will be divided first. For example, when my father-in-law dies, half (that is, a quarter of the property rights) is given to my mother-in-law, and the remaining quarter is my father-in-law's legacy. If there is no will, it will be inherited by legal heirs, including mother-in-law and two daughters (if there is a son, it is also an heir).