These are humorous extensions of common phrases.
1-- That’s the way the ball bounces is a proverb-like standardized utterance used after a misfortune and suggesting that we should accept the vagaries of fate. Balls bounce as they must: sometimes they bounce into windows.
Sentence #1 suggests that people who use this phrase and thus take fate rather lightly are often the same people who caused the unfortunate incident (to drop the ball = to fail to complete an assignment or effort).
2-- Grandmothers have a second chance to ‘be a mother’-- to experience the pleasures of motherhood-- when they take care of their grandchildren. (A rather one-sided opinion, to my mind!)