The answer to your question is that if the performance rights fees are paid to the respective organizations, then there is no liability for copyright infringement. Except:
1. There is a third performing rights organization: SESAC. So, check the song list to be performed by the various participants.
2. A new arrangement of an existing song is not protected by performing rights fees, paid to any organization. The performer will require a special license to re-arrange the song. Example: The song, "Blue Moon" was written in 1934 by Rodgers and Hart. The song has been covered by practically every famous singer who has ever lived. Everyone's arrangement is always different from the original. And, while the performing rights fees will cover the live performance, the fees won't cover a new arrangement. So, there is a risk, if a performer decides to completely re-arrange an existing song -- though the risk is primarily on the performer, not the promoter. Regardless, if you are really liability averse, then you will require that anyone who performs a song in a manner other than exsctly as it was originally performed, obtain a license from the copyright owner.
I hope I've answered your question. Please let me know if you require further clarification. And, please provide a positive feedback rating for my answer -- otherwise, I receive nothing for my efforts in your behalf.
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