Don't worry about it! I'm happy to answer whatever questions you have.

1. Yes they can!
2. I can't think of any canon evidence of them being able to do this, so I'll say no for now.
3. Yukine is shown learning spells within a few months, but Yukine is a quick learner. I would say that the simplest spells can be learned within an IC month, and that would be a spell like "Bind". More advanced spells would take longer to learn, obviously.