If you’re serious about your band, then it is worth the expense of paying an entertainment attorney to draw up a legal agreement so you can set the parameters of your partnership right from the start. Otherwise, you’re setting landmines for yourself in any future dealings between you and your band mates. If you’re all professionals, approaching the band about this shouldn’t be difficult. The time to draw up such an agreement is as soon as profits are going to be made.
You must contact the song’s publisher or publishers to get permission to sample a song. Publisher information can usually be found in the Performing Rights Organization websites. You’ll likely have to search within the PRO with which the song is registered.