All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
There is no doubt that seeing those films is a kind of Zina (fornication or adultery) as the Prophet said: “…Eyes commit Zina and the Zina of the eyes is by gazing…” [Muslim and Ahmad] However, a person who sees those films is not obliged to perform Ghusl (ritual bath) if he did not discharge any sperm (Maniyy). Similarly, he is not obliged to perform ablution if his ablution is not invalidated by discharging preseminal fluid (Madhi). Even though seeing forbidden films is forbidden, but this, by itself, is not one of the things that necessitate Ghusl or something that invalidates ablution unless this is accompanied by discharging Maniyy or Madhi, because if there is a discharge of Maniyy, it is an obligation to perform Ghusl, and if there is a discharge of Madhi, it is an obligation to completely wash the penis [and then perform ablution].
However, your brother is obliged to repent to Allaah because looking at forbidden things spoils one’s heart and subjects the person to the Wrath and Punishment of Allaah.
For more benefit, please refer to Fataawa 85700, 82765, 84093 and 82245.
Allaah Knows best.