Undergraduate / "The Mindset" Why Engineering?-Columbia Supplement [3]

1) The middle of your essay does a good job bringing out the way you see engineering. The lack of an 'ah-ha' moment is ok since you seem to develop that your fascination with engineering probably began when you were younger

2) Just a point on the three E's: economic is an adjective and doesn't quite fit in with the surrounding nouns (effectiveness and efficiency).

Undergraduate / "Dad is leaving", "My country", "Nuclear engineering" - MIT prompts [2]

"my brother rushed into my room, shouting and that's when it all began."

Perhaps end the sentence after 'shouting' and start the next sentence with "That's" to create a stronger impression

"For months I waited for him but in vain"

How about just "For months I waited in vain"
It's already implied that you're waiting for Dad

You don't need the words "it was" before 3d modeling - it creates a comma splice
Also, I believe there should be a "-" (dash) between 3 and d since it's short for 3-dimensional

"I did the seemingly impossible I started a business in a developing country, at the age of 14 and pulled my family back on their feet."

Try adding a colon ":" after impossible and removing the comma after country so it looks like

"I did the seemingly impossible: I started a business in a developing country at the age of 14 and pulled my family back on their feet."

Scholarship / "I need financial assistance" for scholarship about academic and other achievements [2]

"who really need to pay for their education in university" might be better reworded to "who could really need help in paying for their university education"

"Since I discovered BSU, attending this place has been my fondest dream"

"this place" sounds somewhat awkward. Perhaps try "Since I discovered it, attending BSU has been my fondest dream"

Undergraduate / Is Humor Unnecessary (Aerospace Engineering)? - Boston University [8]

Your response to the first short essay seems to be a bit too general

Try mentioning more specifics about your interest in the school such as what about the "you-at-bu" video or the perspectives on student forums that caught your eye

On your second essay, just watch on the last sentence where you switch from the singular "I" to "we"
It may be your intention, but I think leaving it as "I" keeps your essay more personal