we are both open with each other
Unfortunately you are learning you are not. Teenagers keep secrets and tell lies to cover their tracks. Completely normal.
She is only 14 and has been scammed and is now terrified of the consequences so still choosing what to reveal. She knew it was wrong, that's why she hid and is still hiding it, she just didn't understand the full enormity. Now she does it is time she came clean.
If it was ds I would not be going berserk, but it would be a very firm conversation with no space for naps or giving time overnight to make up a story, the truth doesn't need time. I would make sure he understood he has been taken advantage of as a child, but he has also done something stupid and illegal accepting this money and it needs to be fixed. I would explain it isn't about getting friends into trouble, they have been taken advantage of too by the wrong type of people, this could get out of hand and children hurt, and the police/parents will be finding out anyway. I would be insisting on full disclosure now so I could support him before the police arrive - he would be grounded with no phone/internet until I get a full story with no holes in it.
I would involve the police, I doubt they will be interested beyond taking a statement but you need to know what to do with the money. Involve the school. I would remove his access to banking until he is older and a bit wiser (25-ish?). Any illegal money he had spent he would need to pay back (either to the bank/police/friend or give to charity), he would not get to profit from this.
I would also contact all the parents of his friends that I know (I know most of them well through football), or I would find them on Facebook, explain the scam, warn them that these scammers are in contact with some of the children and suggest they check their children's bank accounts and pass onto other parents to do the same. Tell them to contact their banks, police and school if they find unexplainable large transactions.
If you don't want to say it is your dd then say you have heard from another parent.