The square root of number 121 is "11". What is the square root of the number "12345678987654321."?

Can you decipher these quotes by Albert Einstein?
Blf xzm mvevi hloev z kilyovn lm gsv ovevo lm dsrxs rg dzh xivzgvw.

John and Jenni are a married couple. They have two kids, one of them is a girl. Assume safely that the probability of each gender is 1/2.
What is the probability that the other kid is also a girl?

Hint: It is not 1/2 as you would first think.

Who has married many women but was never married?

People put me on the table and cut me but do not eat me. What am I?

The centre of the third figure is empty. What digit should fit inside?

I make two people out of one. What am I?

What can you catch but never throw?

I travel all around the world but always stay in the corner. What am I?

Dwayne Johnson was running away with the loot from a heist in his car along with Vin Diesel. One tire was punctured and he dropped down to replace it. While changing the wheel, he dropped the four nuts that were holding the wheel and they fell into a drain. Vin Diesel gave him an idea using which they were able to drive till the rendezvous point.

What was the idea ?