When you say that they hold the username and passwords on those sites, are you referring to the domain name registrations or just to the web sites themselves? If your customers own the domains, then the server (web site) usernames and passwords don't matter, you can still transfer the domain names to a new host. If you mean the usernames and passwords for the domain name registrar (some registrars have them) then you need to contact your registrar directly and should be able to get that info assuming your customers were listed as the owners. If they aren't, then you have a problem :-(
Who are the names registered with, and who are the owners?
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