The Al Nassr striker chose not to attend over concerns his presence would overshadow the day.
Sister Katia took to social media to explain why Cristiano was absent amid some criticism from the Portuguese public.
Katia wrote: "When my father died. In addition to the pain of loss we had to deal with a flood of cameras and curious onlookers at the cemetery and everywhere we went.
"And attention was not what it is today in terms of access... At no time were we (the children) able to leave the chapel; it was only possible at the time of the burial, such was the commotion.
"At the funeral, there were presidents, coaches of the national team at the time, such as Luís Filipe Scolari, etc. I don't remember seeing any of them. And they certainly greeted me. The pain blinded me."
Criticism of my brother is tiring
Katia also said, "About pain/family and real support... You will never know what it means until you go through it. If someone sends me a message criticising anything my brother does, I will block it (completely ignore it), that is, they will only do it once.
"It's getting tiring. The fanaticism. The criticism for nothing, I repeat nothing... Sick society... We all have families.
"It is absurdly shameful to watch TV channels/commentators/social networks emphasising an absence (wise) rather than respectfully honouring the pain of a mutilated family destroyed by the loss of two brothers. I am even ashamed to watch.
"And so the world goes... Society and opinion. Today they are worthless. They themselves have become bottomless pits. I feel sorry... And war is also like that. Believe me. Human evil is also a war. And every day we have to fight against it. And so it goes."