Do I have a case? I'm going to sue for illegal use of copyrighted music!?

So, my father ped away a few months ago. Before he ped away he was getting ready to sue people for using his copyrighten music. Here's what happened, he was in a band & he had helped write music for the songs as co-author of the music. Well he had all the music he had helped write, copyrighten. So August 8th of 2000 he had 4 songs music that he had written, copyrighten. Well he ended up getting into it with the band and telling them they could not use the music he had written in their cd. Well he thought that was the end of it. But a few years later, someone annonymously sent him a cd from the band he had been in. They ended up using his music anyways! They didnt know my dad had copyrighten it. They included him in the cd, BUT never gave him any royalties. He, by the way had his music copyrighten through the library of Congress. So he was planning on sueing them for lost royalties and everything else he should have gotten but didnt. I am the only child and everything got left to me. I'm planning on pursuing this but just wonder if anyone thinks I would have a case? He had 4 of the songs music, on the cd copyrighten. I am also wondering if anyone thinks a lawyer would take this case for contingency? I don't have the money to pay a lawyer but realllly want to pursue this. On some of the copyrights, another man in the band is listed as co author to the music. Will that matter? Please please please help! Thanks!