Alucian can be found either in the garden, library working on your project or tutoring you, or at the infirmary. I recommend making sure your intelligence is high enough (at least 10 i think?). To get prompted to work on the project with him you need to attend a class with him, i think its alchemy. Make sure you're honest with alucian such as not doing well with the project and about his eye sight, that's what he prefers.
For Alucain, I managed to get his success ending in about 3 tries? I followed the advice of having more than 10 INT before the completion of the project. I also spent most of my time in the library, and I suggest when the tutoring pops up, you choose it as it's often Alucain who tutors you then right after that choose the library again to work on the project with Alucain. Just keep on repeating that sequence and you'll get his success ending.