Is it the bifold doors that is making the space feel tight? Or is there poor access to the closets, because the door opening isn't as wide as the hallway? An overhead drawing with measurements would give a much better idea of what you're dealing with.

One option would be to remove the doors, and add shelves, drawers and hanging rods to make the most efficient use of the closet space. If you live in the Midwest, Dakota Closets at Menards are versatile and easy to install. I've put them in 4 closets, with good results.