They have close registration date. All of them are 19 years old male from Bangladesh. One of them was already red tagged for cheating bounty with alts and now they send ethereum to each other.

Some might call it a coincidence. But I see it as: one of the ethereum address is so called "bank" and he sends ethereum to others so that they have funds to pay for gas.

Maybe I'm wrong and what I found is not a proof but just a concatenation of circumstances.