Proof would be easy to obtain for Fizzer. I believe he can check whether they log in from the same IP Address.
That said, while I get Hell's point (coin games need to be cheating-free), Fizzer's noticed this now and it's up to him to act on it. I'm pretty sure he will; coins look like something he put thought + effort into to monetize the site; he has more of an incentive than anyone else to preserve the legitimacy of coin games/tournaments. I think it's safe to let the issue go.
^ I mean, reporting something on the forums have not lead to any action taken by Fizzer in the past. If you believe that anyone has violated the WL ToS, reporting them is the only way too,... well... report them xD
The coin games need to be more transparent. At this time there is no public record of the games a player earns coins from; like the ladders, there should be a running list of finished games. A player's total number of coins should also be public knowledge.
Since I'm quoted above, this is the reason why I believe they may be the same person:
Arlecchino & Teonanacatl played the 2v2 ladder together and often took their turns closely one after another. That's of course not proof, but typical alt behaviour. Arlecchino was mostly first, followed by Teonanacatl unless the turn was taken immediately (under 15 minutes) when Teonanacatl was first. This would be consistent with the "logging in with the alt to take the turn" idea. Only one account said gg in our game, supposedly the main account Arlecchino.
Their playing styles are / were very similar as well and me and Yeon actually assumed they were the same person from the start and never got any indication of this being not true.
I agree with knyte though: Coin games are important for Fizzer, so it's for his own good to look into it and he probably will. Other than that, it's pretty pointless to discuss it here.
Nevertheless, people are innocent until the opposite is proven. We, nor Fizzer, can rule out the possibility that they are brothers, a married couple, father and son, ... In short, they may be roommates or family members and playing from the same computer. Even if the accounts were originally made by the same person, it would still be OK if they are handled by two different legal persons now. Taking away coins, banning or something similar could get problematic for Fizzer if it turned out they were doing nothing wrong. So I think it's best to leave this to the staff to handle in the most careful way. Like someone said above: if you want to do something about it: report them and the staff will look at it. Making topics with caps lock and with alts may not improve the situation, I think.
As a final note: didn't we have to input our birthday and country of residence to get the free coins? (I may recall this wrong?) If this was the case and they did, it comes down to 2 options. If their birthdays are the same, Fizzer has his proof unless they can show they are twins. If their birthdays were different, it should be very easy for them to show Fizzer 2 ID's matching the birthdays to prove there is no cheating. But this is something that can be discussed between the WL staff and the respective accounts holder(s), that information should never be public.