Is it obligatory to perform ghusl (ritual bath) after janabah (state of ritual impurity due to sexual activity), including thoroughly washing and running fingers through the hair, every time after frequent intercourse? And what is the correct method for ghusl?

Ghusl (ritual bath) from major ritual impurity (janabah) becomes obligatory when the time for prayer arrives, or when one intends to perform an act that requires ritual purity. If sexual intercourse occurs repeatedly before performing ghusl, then a single ghusl is sufficient, because ghusl is not required for each instance of intercourse unless one has already performed ghusl for the previous one. An-Nawawi and Ibn Hazm transmitted the consensus that a single ghusl suffices for repeated instances of janabah. Long hair is not an excuse to omit washing it; rather, it is obligatory to wash it and ensure water reaches its roots, even if ghusl is performed multiple times. Islamic law permits not undoing braids if water can reach through them.