Is it illegal to share publications not in the public domain with collaborators?
So is any of this legal?


Unless your sharing falls under fair use in your particular country (and with the Internet, sharing online is a tricky business anyway), you should not share the papers.

If you want to share the papers, linking to the original source is the best option, and Google Scholar or other online repositories can get you pretty far with a lot of material.  If you can't find an online source, you are limited to providing a cite and hope that whoever wants to find the article can use their library to source it.


  If not, what are the possible repercussions for me personally, and for the people I sent it to?


Practically?  Unless you are sharing the files openly to a broad audience (i.e., so they are available online), no one is going to track you down to sue you.  I would avoid linking directly to articles that aren't behind a paywall, but emailing them to people you are collaborating with is unlikely to cause you any trouble.