Solution:

Eggs

Dinosaurs laid eggs long before there were chickens

Solution:

Playing chess

Game needs two players so Brother-8 is playing chess with Brother-2

Solution:

This is more of a philosophical question than being a riddle or a puzzle. The action of Brian directly led to the result which is the death of Chris. Thus he murdered Chris. In a sense, Chris died due to the lack of water. It is the circumstances that ultimately led to his death.

Solution:

It can be down as shown below.

Solution:

It can be done as shown in the picture below.

Solution:

888 + 88 + 8 + 8 + 8 = 1000

Solution:

The person on 73rd number will survive.

Explanation:
Till the number is the power of 2, the last person to survive will be the one who started it. But since the number here is not the power of 2, we will take the greatest power of 2 that is less than the number which is 64.
100 - 64 = 36
36 people are killed as 2, 4, 6, ..., 72. Thus the sword will now be given to the 73rd person. Now he is the first person to start in the remaining 64 people. Thus he will be the one to survive.

Solution:

A
D
C
A
B

Solution:

Put one red marble in one box and all other marbles in the 2nd box.

Probability :
50 + 24/49

Solution:

Kid1, he was left with one rock.

Solution:

   9567
+ 1085
======
 10652