I'd say it varies to be honest. To me it depends wholly on what people like about a band: if it's the lyrics that carry it, i.e. Gaslight, then, yes, the songwriter should receive the lion's share (especially if the songwriter also writes much of the music). But if it's the guitars that carry it, i.e. Versailles or DragonForce, then the money should go to the guitarists. In your case I think you should purely because so much of the band is you. Morally, that is.
Practically, it's a bit awkward to work around, so until the money involved is big bucks I'd recommend asking for a token amount more than the others. This way, there's a precedent set and you can always make a case to increase it if you find their efforts lacking.