Legally obtaining permission to use music

Safest bet is to not only get each member's (as each member contributed to the whole of the piece and has a stake in it) but also whomever wrote the lyrics and whomever wrote or collaborated on the music if printed notation exists. The fact that the band may be defunct has no bearing on the copyright individually or collectively.

I get the lable's permission. If they are not signed, have the dude who wrote the song sign usage rights over to you. Bottom line, whoever owns the song, that's who ya go to.