I'll try out a collab.
I would help think up the settings, twisting tropes, and build up the characters.
I don't quite understand this question, but I hope to stick around from beginning to end.
Character plans: Personally, I've seen enough of the twins who are the same/opposites get played out. Maybe have them as fraternal twins (have similar looks). I always wanted to try out writing an extroverted person with anxiety, Casey could have that, with a desire to prove himself in whatever he's interested in, and determination. At the start, is awkward and makes a lot of mistakes. Later on, learns not to let his fears control him (though he's still afraid) For Andrew, he's someone who isn't usually noticed at first, but has good intuition and has shown to be the man behind the man in groups and comes across as the most emotionally controlled. Actually feels like he's more impulsive deep down, which has caused problems for the people around him when he was younger. Needs to learn to balance his random side and controlled side.
Plot plans: Unsure, this will depend on the genres - comedy-mystery, dark/horror-mystery, crime mystery, as well as the themes and main question of the story.