It's no wonder they felt that way. Although serving their mother in such a manner was thrilling, it still felt a bit awkward.
But if Ye Fei joined in, it would be a completely different story.
Whether it was watching their brother thrust his manhood into their mother's private parts or having their mother watch as their brother did the same to them, it would be incredibly exciting—a bit perverse, but extremely thrilling.
Ye Fei was somewhat disappointed that his mother didn't let him have sex with her, but he understood her consideration for the bigger picture.
Neither Shui Ying nor the three sisters were inferior to his mother in terms of appearance or figure. After practicing Xuan Yin Art, their private parts had all become top-notch.
Even if having sex with them wasn't quite as satisfying as with his mother, it was still incredibly pleasurable.