At the end of the day, seek legal advice. A lot of people will tell you to put it in the "too hard" basket, however I'd seek advice from the professionals. You'll find many law firms, including the big ones, will conduct an initial assessment of your case free of charge. A lot are also promoting their "no win, no fee" policies in order to remain competitive, if they have a good chance of winning (or reaching a settlement from the defendant), they'll run with it.
If you do consider legal action, be careful on what you discuss in public with respect to the case, defendant or the allegation.
Copyright is automatic on all written and created works.
Correct.
...but since the author had licensed everyone who has his kit without a contract, they can use it however they want, including creating copies.
No, they cannot. It doesn't give anyone unlimited rights to blatantly rip-off the creative works of another. Copyright can be implied which means you don't need to necessarily include the 'Copyright' disclaimer.