I had to pop over in part to offer support. I too have a tough sleeper, well past the toddler years, and it's tough.
I too used the reward system with my little guy, and wanted to say that starting very very small was the only way we found it effective. Saying zero cry outs for an entire week is completely unattainable in his mind, so even trying, is futile. We used a very gradual approach. We would have a small reward for calling us back many times, but only needing a cuddle of 2 minutes or less, then after a few days, we'd up the requirement and he'd get the reward for only calling us back once or even twice depending on the frequency of the initial wakings,(crying out and putting himself back to sleep didn't count against him, in my mind, that's a total win),then continue on with requiring more and more sleep from him to obtain the reward.
also, are your boys sharing a room? I was completely terrified of letting my terrible sleeper share a room with my rockstar sleeper out of fear that it would ruin the one good sleeper I had, However, I found that having the company of his older sibling in his room, made DS2 feel a little better. And, surprisingly enough, DS1 slept through a majority of the wakings, or on some occasions, I'd even hear DS1 tell DS2 that it was still night time and to go back to sleep. When DS2 was old enough to have his own bed, he'd even go lay on the floor next to his older brothers bed and would find comfort in having him close. It was scary at first, but for us, we did find it somewhat helpful. Also, we put the boys together right as DS2 was nap dropping, but we found that allowing DS2 a short nap each day, extended his day so that he could go to bed at the same time as DS1, and that helped DS2 feel more comfortable in his room and They often fell asleep "talking" to one another.
Good luck! Hugs! I always had in my mind that surely he won't be waking when he's 2 or 3, and then when we got to the point where he was, I was so discouraged. I hope he gives you some peace and sleep soon!