It's a given that DRs are fake in this style of BB. Like the one Sarah had in the latest episode, was it about Sabrina, I've forgotten already. I'd guess the producers have strong input on the DR script.

The producers definitely script some of it, but I don't believe it's all scripted/fake.

They will ask certain questions to steer the houseguests into saying what they want them to say, which ultimately I guess could be considered scripted. The houseguests talk about it all the time, such as "you know X situation is gonna be on the episode, you can tell because they've asked me dozens of questions about it."

Then there's the actual literal scripted situations like with Neda last week. She said producers forced her into saying something she didn't want to say in her goodbye message to Ika. I'm guessing it was something negative because she felt bad about it. Mentioned it was about the letters, but didn't say exactly what. Don't think that part of Neda's goodbye message got shown in the end... I can't remember it anyway.