How can I create a new user but with a home directory that already exists?

You did create a user with a home directory that already exists.

adduser: warning: the home directory already exists.
Not copying any file from skel directory into it.

This isn't an error, it's a warning. Usually, the reason not to create a home directory is for a user whose home directory isn't supposed to exist. Here, it does, which has a high chance of being an error by the system administrator (e.g. a bad copy-paste or a buggy script). Since you really meant to use an existing home directory, ignore this warning.

[root@LinuxAcademy ~]# su Jerry
bash-4.1$ bash: /home/panos/.bashrc: Permission denied
bash-4.1$ 

You did log in as Jerry. That bash 4.1 is running as Jerry. Jerry doesn't have the permission to read his ~/.bashrc, either because the file .bashrc is only readable to panos (and perhaps to a group that Jerry doesn't belong to), or because the directory /home/panos itself is not accessible (x permission) to Jerry. So bash tells you that it can't read its startup file, and it displays its default prompt.

Having multiple users with the same home directory is very unusual (excluding system accounts whose home directory doesn't matter). What you should do about permissions depends what you're trying to achieve by this. You probably do want to at least allow all these users to read their home directory.

Well, of course. It's trying to read and execute /home/panos/.bashrc. That file belongs to user panos, and presumably is set to -rwx------ or something like that. So Jerry tries to read it and can't. Permission denied, just as it says.

It's possible that Jerry actually is logged in. Try whoami.

So, put them in the same group and make it group-rx, or make it world-rx, or something like that. And do the same for the home directory (executable, for a directory, means searchable).