Solution:

I Over Ate

Explanation:
Check the mathematical solution on the image below.
Also, 8 in 2018 resembles a fat person.

Solution:

One Night Stand.

Explanation:
Number 'One' + Knight(chess piece) + st + and(symbol &)

Solution:

199 - 99

Solution:

The brain teaser can be solved as shown in the image below.

Solution:

7, 4, 6, 5, 8

Solution:

4 6 5 3 (from magician perspective)
3 5 6 4 (viewer perspective)

Detail:

From user perspective:
3 5 6 4 => 5 6 4 3 => 6 5 4 3

For magician perspective
3 4 5 6 (ascending order as)

Solution:

Michelangelo juggles the diamonds across while crossing the bridge.

Solution:

Can be found on the pic below.

Solution:

They use the bricks and dirt from the tunnel to stand on it.

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:

step 3 is wrong