when we throw an egg and a watermelon from the same height we observe that both hit the ground at the same time but when we throw a brick and feather from the same height we observe that the bricks falls earlier than the feather. we are on earth. how is this possible because we know that g is the same everywhere?????/

Gravitational force of attraction between two bodies always depend on their masses. However, the acceleration due to gravity does not depend on the mass of the body.
During free fall, the heavier objects as well as the lighter objects fall with the same acceleration towards the surface of the earth, since the acceleration due to gravity does not depend on the mass of the body. The slow speed of feather, while falling, is due to the fact that its surface area is very large as compared to its mass, so the feather experiences much more resistance from air and its speed is slowed down. However, the brick, being small and heavy, does not get much air resistance and falls to the ground at a faster rate.