Is this it okay for my sister (14) and my best friends brother (17) to date?

*ALL OF THESE ARE FAKE NAMES*

Bestfriend= Sarah

Bestfriends brother= Eli

My sister= Emma

Me= Ally

BFF brothers girlfriend= Amy

My sister's boyfriend Cooper

So, a little background knowledge, Sarah and I have been friends for over 6 years, and I have been over to her house multiple times. No one in our friend group likes her brother due to the fact that he is a very rude child to his very kind parents. (And yes, they are very kind this isn't them acting.) When Emma meet Eli he was in a relationship with Amy, Eli and Amy had been off and on for a while.

Emma had been in a relationship for about 6 months with Cooper; they were very happy long-distance, and Cooper even bought her a promise ring. (They were long distance.) Cooper and Emma had broken up twice due to allegations of Emma cheating. (One being a dick pic.)

So over the past month, I noticed that Emma and Eli have been getting closer, so I did something I am not proud of I went through Emma's phone. (She had been arrested for sending nudes out so she didn't have much electronic trust) I found photos of them and how Eli knew Emma was still dating Cooper. I also found sexual photos. Eli had also been cheating on Emma with Amy. I told Sarah and she was shocked and so was I.

I just don't know what to do please help.