Trouble testing sandbox

I am trying to set up a sandbox to see how the Donate button might work on our website (cincinnatifriends.org/wp). However, I can’t seem to get past the first page. I can’t log in using either the actual PayPal account or the personal or business accounts that I set up on the PayPal development site/sandbox.

I’m also concerned about the email account that appears on the page, which is that of our treasurer (who created the PayPal account). Is that how the page will look to individuals making a donation? I would prefer not to expose our treasurer’s email address in that way; it seems like the donation is being made to an individual rather than to our organization.

I tried reading through the PayPal documentation, but didn’t find it very helpful. Any suggestions on what I need to do to test the Donate button?