Admin for single site installation

Yes, that’s possible. Once the site is set up, there is one default admin (the one stated during the installation). That admin can create a new user with admin priviliges.

When you look in the User menu in the admin, you can list all users, and easily see the roles they have (administrator, editor, subscriber, etc.). Once your developer is done with the site, make sure his user account is either deleted, or changed from administrator to something less.

Is it possible to have two admins for a single site installation?

Yes, this is quite normal.

He says I could delete his ID after the website is complete. Is that correct

Yes. You could delete it, downgrade its role, or change the password. All of these will effectively disable the account.

is there a way to find whether any other id exists super-ceding the rights of these two ids?

Yes, from your WordPress login Dashboard, select USERS, all your users will be listed, you will be able to see which are administrators. There is no super-admin as such, except for access to the web hosting management (which is not WordPress), the web hosting manager can manipulate the files and databases that run the website, there are various circumstances which require the intervention of this administrator, knowing who has this access is important.

Thank you.

You said it is important to know who has access to the web hosting management. If I have the website hosted on godaddy and I have the password to the web hosting then this person you mentioned would be me. I hope that is correct.

Not necessarily.

You are the person who has access to your files, using your GoDaddy username/login.
You also have access to your WordPress dashboard, using your WordPress username/login (that’s a different account).
There could be others who can access the WordPress dashboard, with their own WordPress username/login — this would be the developer you mention in your original post.

What @rossmitchell meant, is that the people at GoDaddy have full access to everything you host on there. They can do anything with your files and database they want. That sounds super dangerous and evil, but rest assured they will only do this when you request help from them, when things are seriously messed up.

Yes, it’s you. I think DSketch was just answering your question about “find whether any other id exists super-ceding the rights of these two ids” saying there are no super-ceding rights in WordPress, but the account that accesses the host could be thought of that way.

I looked up the visitor details and saw the following:

->/
->/wp-admin/admin-ajax.php
->wp-admin/admin.php
->/wp-login.php?redirect_to=http(…)m/wp-admin/admin.php&reauth=1
->/wp-login.php

And the above is not me. Does the above show that someone is able to access the admin area?