When they created an account or what they had in common in terms of betting pattern or activity in your site makes no value for us forum members. However, the above quoted blockchain transactions are enough to conclude that all three accounts are either the same person's or three individual users'. Imagine a friend had bitcoin and other do not know how to handle bitcoin. The friend who has bitcoin can help them. Baseds considering these transactions we can not say that StackGamblerm is giving us wrong information too about his friends accounts. The accounts can be owned by them friends.
It is common policy among Bitcoin casinos that accounts cannot be funded from the same private wallets. This rule is in place primarily to prevent multi-accounting. With the prevalence of VPN (many undetectable), it is no longer as easy as "same IP, same guy." The blockchain is one fingerprint used in determining the unique identity of someone. Saying that a friend with Bitcoin can help them is great in theory, but it is comparable to saying that the other login from my IP is from my roommate. It doesn't guarantee a multi-accounter, but is one tool that is used in taking steps towards a resolution. We also detailed several other ways that the accounts are related in out initial reply, which have been confirmed by OP.
What is your multi-account policy? I assume suspending the account with refunding the deposit or both winnings and deposits?
If this is only refunding the deposit then we are fine since you already asked them to get the refund. But if this is both winnings and deposits then you need to give their winnings too.
why did you KYCed them
We will answer both of these here:
https://www.betcoin.ag/support/betcoinag-terms-service7.1 Each player can create only one personal user account. There can be no more than 1 account created per household. Creating multiple user accounts will lead to termination of the accounts. All betting accounts you try to open may be blocked or closed and any bets may be voided. Depending on the severity of the case Betcoin.ag holds the right to withhold or take any funds deposited to pay for damages and/or the prevention of future misconduct.
The KYC was used as a way of determining the severity of the offense.
We understand that a service wallet was involved here. However, the service wallet funded a private wallet, part of which was used to fund Majesty's Betcoin account, part of which was sent to another private wallet, which was used to fund Chiefleak's Betcoin account.
https://imgur.com/a/RrGwjVR