I found my 16y/o brother on Grindr

Hi, I really need advice on what to do and I will start with some context, because it goes way deeper than only being on Grindr.

My younger brother has had an avid issue with unrestricted internet access. I first discovered proof of this when he saved gay porn on my parent's phone at a pre-pubescent age (he did not have a device of his at the time.) Then, it started with instances of having much older online friends where they would engage in sexual roleplay. I found this while checking his devices and forced him to cut off contact and told my parents. I have been the only one to consistently discipline him for as long as I remember - they only reprimanded him short-term; he was not restricted from the internet, his devices were not taken away nor were his accounts deleted/disabled. I then started to be the one to take away his devices and to actually restrict his access to the internet - it doesn't work as he does not respect me and will harass me and take back devices, log me out so I no longer have access, and physically retaliate in some cases. Every single time, it ends with his issues never being properly addressed, as my parent's initial reaction is to yell at him and the cycle repeats. I have been the only one to continuously monitor his internet activity as his older sister. My parents have essentially given up on disciplining him as he's grown older, as he does physically and verbally retaliate against them as well.

Ever since then, every couple months I continue to monitor his internet access and I read his messages to make sure he's not doing anything illegal or irrational. Continuing on, I post this in r/lgbt because he is a closeted minor. I've always declared my support for him and I would never out him or put him in a dangerous position as our parents are homophobic. However, while doing a routine internet check, I found out that he's been on Grindr falsely posing as an adult and sexting adult men. I'm not too sure if he's gone out to meet with them, but he did indicate that he snuck out to meet up with someone (+ engaged in a sexual activity), as referenced in a conversation with a friend. As I read deeper, I also realize that he's been sexting other people of "his age" (obviously there is no way to verify this) and sending them nudes, sometimes with his face in it.

I have caught him doing other unrelated things, such as giving out our address to strangers on Reddit and being unsafe online in general. He is very obviously grown enough to know that what he does is wrong, and I've tried to educate/discipline him multiple times but he doesn't listen. Now that I found out he's been sharing nudes as a minor, I believe I have an obligation to let my parents know that my brother is engaging in reckless behavior online, and I do care for his safety and I don't want to see him harmed in any way. I'm not really sure how to go about this, because I know the moment I tell my parents they are only going to respond with anger, and I fear things may not end well. Apart from my parent's negligence to properly sit down and discipline him, his friends also enable him into doing such things and they influence eachother to do similar dangerous things as well. I cannot tell you the amount of times I've tried to pause his internet, take away his devices, and lock his computer setup up to no avail; either he shrugs it off and continues to sneak to grab them back, physically retaliates or my parents do not hold up any discipline and forget about the punishment.
How should I go about this? I've always tried to be a pillar in my brother's life as his older sister, but it gets to a point where I cannot keep these secrets for him because it will put him in danger.

I appreciate any advice I can get, I care for him deeply despite his recklessness and I want him to realize that ultimately, he should never do this again and to learn from it. ❤️