Confusion about dual license (MIT/GPL) javascript for use on my website

Question

I've read all of the posts I can find on this and I'm still not sure of the answer.

I'd like to use a jQuery plugin on my website that is dual licensed under MIT and GPL.

1. Does the dual license mean that as long as one or the other is satisfied I'm fine, or does it have to be both?

2. I've read that a GPL javascript being loaded on someone's broswer doesn't count as redistribution, so I wouldn't have to use the GPL license for the rest of my site (provide source code). Is this true?

3. My partner thinks I should remove the copyright altogether and change the variable names, as this is going to be on a commercial website. Is this ethical? I respect the person who took the time to write the code. Should I contact them and see if the plugin is available under a commercial license?

Thank you very much in advance for helping to clarify. As this is my first website, I figure it's better to ask these questions than take a shot in the dark.