The first sentence is a set phrase that has the meaning "you are so strong!".
Кремень here is used in the sense of "a hard solid rock/stone".
"Ну" is a particle used to emphasize a sentence.
The second sentence can be translated as "Not so strong... I just have no choice".
Да here isn't "yes", but a conjunction "and", "but".
"Вариантов нет" literally means "There are no options".