When is ghusl obligatory if the menses stopped after six days, and light brown drops appeared for two days, then the white discharge (al-Qassah al-Bayda) appeared on the eighth day? And is the blood that appears a few days after the white discharge considered menstruation or not?

What came down in the last two days is a brownish discharge (kudrah), and it is menses as long as it is connected to the menses and before seeing the sign of purity (tuhr). The eight days are menses, and ghusl (ritual bath) is obligatory upon seeing the white discharge (al-qassah al-bayḍā’). Blood that returns after purity and before fifteen days of purity have passed is irregular bleeding (istiḥāḍah). If it returns after fifteen days, then it is menses.