Yep, for sure it is Ntaj Nplaim Taws. Here's the summary if we're talking about the same movie:
Back when praek and his sister were babies (I think they were twins but not identical) and their parents had two magic sword called Yin and Yang (green and red flame holy sword). The eight family (yim pawg neeg) wanted to own the swords and there were these two bad people. A man and a woman who decided to come together and murder the family for the swords so they both killed the praek's parents and then a xibfwb in white hair (his name is Yawg Yama) appeared and save the baby boy from harm because he didn't know that there was a girl too. So he used his wicked laugh to go against both the two bad pple and when he left, he said that after 18 years when this baby grows up. He will come and avenge the death of his parents and they left. When the bad lady was going to leave, she heard a crying voice and took that baby girl to live with her as her pupil. In her mind she was going to raise the daughter up to fight against her own brother
18 years later when Yang Tachu (praek) grew up into a handsome man, his master Yama asked him to go to the waterfall cave and get the red sword from there. When he finish his mission, he will tell him about his life and his parents so praek left for the cave. Oh his way, there were these two father-daughter villagers. The daughter is Cuab Er and her father is a snake catcher so they were playing around and then these demons appeared in the water and tried to kidnap the daughter. Praek came by and helped them. There was this guy whose name is Tou and he heard that Yin Tachu was going to the waterfall cave, he took his men and tried to find it first. At the waterfall cave, they finally found out that the door was through the waterfall and they decided to fly over there but the two handmen fell to the water turning to skeletons and there came these two female ghosts..etc........(he got the sword, returns to Cuab Er's house, found out that the demons took her by her father and her father dies, he helps her from the demon and let her come along because Tachu promised Cuab Er's dad before death that he would look after her.
Oh their way, they came by some female pupils praticing their sword fights (they were from the Omei Sect which consists of all virgin females) so here comes a snake tomboy who pulled a trick on them and that's why they were throwing the snake around and they accidently threw it towarn Yang Tachu and he accidentally killed the snake.......(things happen again)
He finally meets his sister who was name Yee Tafong but they didn't realize it towards the end when the snake tomboy told Yee Tafong that she wasn't a Yee and that she was actually a Yang. She told the whole incident of what happened to Yee Tafong's parents because the snake tomboy overheard Yee Tafong's master and Tou's master talking about the incident. Yee Tafong and Tou's masters are the one's who killed praek's parents......
In the end, justice was brought they finally avenge the death of their parents.
