(assuming your based in the USA)
For the 'employee' one I agree as well, remove the splash page if your already using a PSK for that. Should solve that issue at least.
First let me say that I am not a lawyer. What I am is passionate about seamless wireless =P
If your legal department for the library says you need one then by all means, follow their instructions accordingly.
However because your going to have a splash page your going to run into issues like you've stated, which is why myself, and other wireless people in the industry are so against them.
As for the whole captive portal/splash page thing.
I use to do work at a large university, many thousands of students, very large, thousands of access points. They would get a letter in the mail almost weekly about mis-use and users downloading content and tormenting etc. First time I saw this happen, the guy opened up the letter, realized what it was, and walked over and tossed it in the trash.
From all the discussions I have had with other wireless people, the captive portal apparently doesn't serve any real legal purpose. It might make management/legal department feel at ease, but otherwise from all I've talked and read about, that's about it (other than cause issues for IT department lol).
It certainly is a debatable topic, with people on both sides of the fence, but that fence has been leaning more and more towards getting rid of them as time passes, and wireless becomes a staple everywhere.
I would certainly advice that it might be in your best interest to implement content filtering at a minimum, to avoid people from being able to torrent and what not. That I do recommend.
Bottom line is anyone can TRY to sue for this, but winning the case is another story. Has yet to be done as far as I've been able to find online. AUP/ToS page isn't going to stop it from happening, so your legal department is going to get good at throwing crumpled up paper into the trash like a basketball unless you start blocking it 😃
Large companies have done away with them, like Apple, Disney, Google, major international airports etc., so that the guest experience is trouble free. If those legal teams concluded it ain't necessary, then the rest should follow their lead haha.
Here are some links on the topic:
I'll point you to this link here, which is worth a read (maybe send this to your legal team lol).
Some interesting links:
Example of how this topic is still a debatable one: