the fact they both posted at the same time, shows 2 different people typing at the same time, you and others getting mad because same ip is same is actually angle shooting and wrong.
Who says they're not two different people
The allegation isn't that they're the same person playing. It's that they're two guys eating Doritos and probably playing in the same room, maybe share monitors and talk about the game, and also never suspect each other.
If these are both fine with your standards of what is good etiquette for the game then fine, but also, none of this information about their arrangement is voluntary. It took months of poking around and for a while they didn't even acknowledge when people called them twins/bros and such.
So it's not just "they have the same IP", it's that they first behaved in a generally untrustworthy matter, coinciding with playing under the same roof, and act appalled when they are suspected
Like I said, trust is not really hard to earn. What they have earned from most of you isn't trust but empathy from boo hoo crying.