Is this grammar correct?

Question

Of the two football players, Herman was the heaviest.

No, it's not correct. You are comparing two people; therefore, you should use "heavier" rather than "heaviest."

In the late 1990s, the popularity of MTV’s The Real World sparked increasingly interest in this concept.

you need to change the word increasingly to increasing. This has to be an adjective to modify "interest", not an adverb.