OK so main set up:
All goalkeepers are DRUMMERS (Because drummers are the backbone of almost every song and VERY important).
Defenders are back be beat instruments (like pianos, flutes, violins, etc, because they are the in the back, but also VERY IMPORTANT TO THE SONG)
Mid-fielders use front beat instuments (like guitars and trumpets and keyboards), because they can be background like the defenders-but they have their role connecting the defenders and the forwards.
The forwards are all, of course, SINGERS! BECAUSE they're at the forefront of all the songs and always needed!
And there we go! Since 11-man bands arent, well, practical or possible, I feel like the Raimon Eleven, or any otther team for that natter, would be like a Studio rather than one singular band: that way, a few of them could play together at once, in 4s or 5s. BUT, the goalkeeper(that is to say, the drummer) would be needed in almost every song, because drums are, again, the backbone of a band!
Song battles between bands/studios go something like this: it goes in three rounds, and the two bands on stage generally try to disrupt eachother's tunes by playing their own! The first to get out of tune would usually be the singers, then the front-beat players, backbeat, and finally, the drummer! If one band can make the other entirely lose their tune, they win one round!
If its a bit difficult to understand, dont worry, I feel you! Just let me know, and I'll fix things around so its less confusing, or help explain it to you! :)