Usually from their dad.
It would certainly be economical. They could use their ma's bras.
No...no....no....my mom looked like a board hit her in the chest....me? Endowed to say the least.
Maybe ... But not necessarily
Not sure but I think breast size is inherited on the male side.
A study in the journal BMC Medical Genetics analyzed data from more than 16,000 women and found a total of seven genetic factors were significantly associated with breast size. “Your breast characteristics can come from both sides of your family, so genes from your dad’s side can affect what your breasts end up looking like too,” Minkin says.
(Much more information in the link)
Some do. Some don't. I wore the same size as my mother when I was in 8th grade. By 9th that was no longer true. My niece and her mother are the same though.