Complex sentence: IFK Landskrona comprised adult players only, and as various competitions got more structured, they needed the formality that existed in Diana, while IFK Landskrona's main contribution to the merging into Landskrona BoIS, was their players.
Split into simpler sentences: IFK Landskrona comprised adult players only, and as various competitions got more structured, they needed the formality that existed in Diana. And IFK Landskrona's main contribution to the merging with Diana into Landskrona BoIS, was their players.