Shaun is the most difficult because though he’s done the most, he gets moody. This is similar to another model who is straight but enjoys gay sex, Ross. So a flip scene with the two might work because Ross can relate to him, Ross’s ass feel like liquid gold and Shaun is an easy dick for Ross to handle. This gives him someone who understands his mindset a little better, and gives Ross the chance to be a mentor/ lead.
Scotty is easier. Just pair him with someone good like Justice or Saint. They are big but not too big and know how to lead. Plus he’s already been paired with Saint, so he’d be more comfortable exploring