Are you trying to crash the server by running over 2 cron jobs a day? The server seems to automatically remove crons that run way too often (not too often, but way too often).
Estimation is exactly that, an estimation, there is no guarantee you will receive it that day. The problem is that java can only be enabled on a limited number of accounts (100 or so), so an account must lose java (usually removed due to inactivity) before another account can have java.
Your domain nameservers are incorrect, they need to be set to ns1.heliohost.org and ns2.heliohost.org. After that, it still takes up to 24 hours to become available to internet.
Why can't these different users create their own cPanel accounts? Giving them FTP accounts to their own domains is another option, if you need to be in control.
Did you just point TK's nameservers to point your domain to Heliohost's nameserver? That obviously doesn't work. Set your domain's nameservers to ns1.heliohost.org and ns2.heliohost.org and it should make life easier for you, but I'm not sure if that would automatically fix the problem anymore.