Certainly, a dysfuctional family dynamic is at play here, and has always been a factor. But at 9-10 years old, it can't be called collusion as far as BR is concerned. Family loyalty, i.e. what will happen to ME if my mom and dad are in jail, sent away, etc. is a big factor. Kids are still very ego-centric at that age. Now, as far as we know, BR is a college student. Still young enough to be dependent on family. His sister and mother are gone, as are his grandparents. Only his father and aunts. (shudder). Of these, perhaps his dad is the lesser of evils.
At the age he was when his sister was killed, I am sure his parents impressed on him VERY strongly the need to keep family secrets.
Remember, housekeeper LHP claimed to have caught BR and his sister "playing doctor" or similar activity; not at all uncommon among siblings. With his sister having been groomed to act sexual in an inappropriate way for a child, and he himself on the cusp of puberty at nearly 10, I would be surprised if it didn't occur occasionally.
Who knows- BR may have been told that his behavior with his sister could put him in jail- the dictionary opened to the word "incest"....
So BR would be old enough to understand the importance of keeping family "secrets". His parents may have been "blackmailing" him to do this, in a way, by saying that if anyone finds out that Mom or Dad were responsible for his sister's death, what would happen to HIM? And if anyone found out that he had been playing "sex games" with her, maybe the police would put HIM away, too.
Only BR knows what he was told. I think the time for him to come forward would be when he is truly an independent adult, possibly when his dad passes away. Not much is heard about the two of them now. When the news about JR and Beth Twitty came out, nothing was said about BR or his whereabouts.