Question about the plot to Blackkklansman (2018) (spoilers, character)

[ironpony]

I just saw the movie and have a couple of questions about the plot:

SPOILERS


Why is it that the two main cops Ron, and Flip, both decide to be Ron? Basically Ron makes a call saying he is so and so, and the Flip goes and poses as that character while undercover. But from then on Ron still pretends to be that character over the phone, even though their voices sound different and are at risk for being caught for that.

So why didn't Flip agree to do all the phone conversations from then on to not arise suspicion? Why would Ron keep doing the phone conversations?

Another thing I didn't understand is in the end, when Ron's captain tells him to destroy the evidence in the case, why does Ron do it? He doesn't want to destroy the evidence, and the police are not allowed to destroy evidence in a criminal investigation just cause the captain says so. Especially when some of the crooks are being indicted such as for attempted murder with a bomb.

So why didn't Ron just go to the captain's superiors and report to them that the captain ordered him to destroy evidence in a case? And go to the prosecutor and tell him as well "hey that attempted murder with a bomb case we handed you, the captain is trying to destroy the evidence".

Even if going to those superiors would not do any good, there is still a chance it would cause it makes the captain look bad if he is accused of ordering his officers to destroy evidence in an indictment case. The captain very well could at least allow the case to proceed to save face then.

So why didn't Ron just spread the word that the captain was trying to destroy evidence?