To whom does the marriage of the seven children fall, with a difference in how they were married between those whose marriage was arranged by their father and those who arranged their own marriage?

The default is for a man to marry himself. The father marries off his son if the son is unable to marry and the father is capable and bears his expenses, based on the statement of Ibn Qudamah: "The father is obligated to help his son achieve chastity if he is responsible for his upkeep and the son needs to achieve chastity." If the sons are capable of marriage, the father is not obligated to marry them off, except as an act of generosity and kindness.