#1
Okay, guys.

Let’s say that I’m part of a five-piece band with myself on vocals/guitar, Evan on lead guitar, Tim on bass guitar, Tom on drums, and Pat on rhythm guitar. All five of us are considered equals.

In the band, there are TWO collaboration sessions during the songwriting process.

Collaboration #1:
I initiate the creative process with the record producer (sometimes I do the same with the lead guitarist and/or some of the other members of the band). The producer and I conceive the basic structure of a song (introduction, verses, pre-choruses, chorus, bridge, and ending). Also, the producer and I generate the lyrics, melody, hooks, riffs, chord progressions, as well as the song’s overall vibe.

Collaboration #2:
The entire band meets in order to flesh out and beef up the final product. The entire band essentially builds from what the producer and I have concocted. The entire band finalizes the arragement, and decides on the instrumentation. All band members provide their artistic input as to how the song should progress. All band members make suggestions regarding the song structure, melody, hooks, riffs, chord progressions, and (of course) harmony. Musically, each band member has free reign over his individual part- I prepare the power chords; Evan the guitar solo and any improvisions; Tim the complementary bass line; Pat the accompaniment and (maybe) additional riffs; and Tom the tempo, drum fills, and cymbol crashes. In no way do I tell Tim which bass line to play, or tell Tom which beat to play. I trust their instincts.

I must mention that in the CD liner notes, each band member has his own “Thank You” sections. Plus, the liner notes contain a blurb that clearly states the following- “All songs arranged and performed by [insert band name]”.

In this scenario- Who should get the songwriting credits? Just myself and the producer? Or the producer + the entire band?
#2
It'll depend on what type of agreement you can get with the band. Generally speaking they'd want everything split equally to be "fair" but you most likely want the credit given to the people doing the most work, aka you and the producer, so you'll have to make your case and hope that they agree with you.

The in-the-middle solution is to credit everyone for exactly what they do, like lets say you credit the drummer for his part, and you credit yourself for the lyrics etc. It promotes team effort and seems fairest.