Do I need to remove all the old paint prior to repainting!
Answer: yes, if scraping and thorough sanding (coarse, then medium, then fine grit) until smooth does not remove the old paint than feel free to prime and paint right over it. 

Do not pay attention to those that say "you must test for compatibility with the new paint" or "don't paint it with latex (water-based) paint if it might be old alkyd (oil-based) paint". Use a high quality exterior primer and a top-of-the-line high gloss exterior paint and it will be beautiful and durable. PLEASE, I cannot under emphasize the importance of using high quality paint brushes, it will make all the difference.