Parents B1/B2 visa renewal


My parents B1/B2 visa is set to expire on 15th May, 2025. I have the following questions, please help me. I trying to post all the possible questions I have to plan better for their visit.

  1. My parents are planning to visit to USA in December 2024. May I know, how early can my parents get their visa renewed? so that they can get their visa renewed and visit USA with good validity.
  2. Do they get dropbox/interview if they want to renew their visa?
  3. Can they apply for visa renewal in USA, if they stay in USA at that time?
  4. As per their visa expiration date which is on May 15th, 2025. Can they visit USA in December 2024 and leave back to India on or before 15th May 2025 without any hassle?
  5. How late can they renew their visa after their visa expires?

Thanks in advance.