The only brother who wanted to save Joseph when he was placed in the pit was Ruben. His main motivation must have been that, as the firstborn, he was responsible for his younger siblings.
18 But they saw him in the distance, and before he reached them, they plotted to kill him. 19 “Here comes that dreamer!” they said to each other. 20 “Come now, let’s kill him and throw him into one of these cisterns and say that a ferocious animal devoured him. Then we’ll see what comes of his dreams.” 21 When Reuben heard this, he tried to rescue him from their hands. 22 “Let’s not take his life,” he said. “Don’t shed any blood. Throw him into this cistern here in the wilderness, but don’t lay a hand on him.” Reuben said this to rescue him from them and take him back to his father.
When Reuben returned to the cistern and saw that Joseph was not there, he tore his clothes.
Joseph was not aware of that fact until his brothers came to Egypt. It was then that he heard that Ruben wanted to save him.
22 Reuben replied, “Didn’t I tell you not to sin against the boy? But you wouldn’t listen! Now we must give an accounting for his blood.” 23 They did not realize that Joseph could understand them, since he was using an interpreter. 24 He turned away from them and began to weep, but then came back and spoke to them again. He had Simeon taken from them and bound before their eyes.
Simeon was the eldest of the conspiring brothers, and that was the reason he was imprisoned.