No. Studies show that a healed fracture has the same strength as the surrounding bone. It is neither stronger and weaker; the one caveat is that there are times during the healing process where it may be weaker and stronger, but once the healing process finishes, it is equal in strength.
No. Once the bones are healed they resume the same strength as the surrounding never fractured bones.
No. There is no evidence that a broken bone heal to be stronger than it was before. Due to the process by which bones heal, there may be a brief period in the healing process when the fracture site is stronger than the surrounding bone. However, they later reach equal strength, and the fracture site is no more or less likely to break again.