Just read it.

Should I return the full double payment, or take my 10% out of it?

Wouldn't it be better, to mail everyone who has gotten a double payment with a different address, so you can keep track of returned funds and who will get the 10% remaining?

Or will everyone get them no matter if he returns them and you just hope all people are honest (which the aren't).

I will return the funds, but I don't want to make you clusterfuck even worse (all returns in one address, some minus 10%, some full), so please send out a mail to all accounts with details.

Thank you.