Hey Dom
I promise you, I know quite well how much it sucks to have anyone, let alone a duo+ flaming you, but there are a few important things to keep in mind.
First, the system does not care how many people report a player in a given game. Once a single player reports, it engages a review. Multiple reports do not stack, nor do they increase the likelihood of a punishment.
Second, all players are held to the same standard. By having an automated system, this is a good thing. While a team of Rioters would have their own biases and opinions, the IFS approaches every single chat log in an identical manner.
Third, mute and report them. Being able to mute someone does not justify being allowed to flame (which some people think), but instead is a justification as to why you are not allowed to flame back. You can press a single button and have a perfect defense against anyone flaming you.
tl;dr: Premades do not have increased reporting power. Stop harassing your teammates for doing poorly, stop flaming people who flame you, or otherwise you'll end up permanently banned.