Learn English – How to describe humanities students in one word

Moralist reproduces the good denotation of gutmensch with a similar dark connotation:

noun

1.0 A person who teaches or promotes morality.

1.1 A person given to moralizing.
_ODO

Almost everyone considers their own morality to be good. Most consider their moral judgments to be superior, or at least on par with the best, but in the modern mind, a moralist is often portrayed with an irrational moral opinion used unsympathetically to cajole and coerce others into conformity against their will.

John Dewey: An Intellectual Portrait, by Sidney Hook, reveals the positive denotation of one who constructs a superior moral framework:

To those who know him by his less technical writings, John Dewey appears as a great moralist and educator.

In his introduction of The Unity of Plutarch's Work, Anastasios Nikolaidis used moralist with the dark connotations of irrationality and coercion:

These findings, however, do not entail that Plutarch was a crude moralist who stigmatized deeds and conducts, meted out prescriptions for correct ways of living or put forward ideal, and therefore unattainable, patterns of behaviour.

Although the preacher from Nathaniel Hawthorne's The Scarlet Letter was predominantly a hypocrite, he was primarily a moralist, who struggled against his own gutmenschlich qualities at the expense of his secret mistress, Hester Prynne:

The days of the far-off future would toil onward, still with the same burden for her to take up, and bear along with her, but never to fling down; for the accumulating days, and added years, would pile up their misery upon the heap of shame. Throughout them all, giving up her individuality, she would become the general symbol at which the preacher and moralist might point, and in which they might vivify and embody their images of women's frailty and sinful passion. Thus the young and pure would be taught to look at her, with the scarlet letter flaming on her breast—at her, the child of honourable parents—at her, the mother of a babe that would hereafter be a woman—at her, who had once been innocent—as the figure, the body, the reality of sin. And over her grave, the infamy that she must carry thither would be her only monument.
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There isn't a generic term that defines classes in relation to a particular student. Instead, we have names for each class in relation to how many years of school they have completed/have left.

In my neck of the woods, students in your example would be juniors and freshmen once school starts.

If this is talking about American college or high school students, traditionally graduation takes four school years. In your first year, you are called a freshman (or "frosh" at some schools), in the second year you are called a sophomore, in the third a junior, and in the fourth a senior. See this Wikipedia article for slightly more detail.

Schools here typically begin in the fall so that an academic year actually spans two calendar years, so those who enrolled in the fall of 2014* would be expected to graduate at the end of the 2017/18 school year. Since it's summer right now, they should have just completed their sophomore year and will be juniors when school starts again in the fall--over the summer they can be called "rising" juniors. Those who are enrolling now will be "incoming" freshmen. Once school actually starts in the fall, you could just say juniors and freshmen, without the "rising" and "incoming":

Hey, you know what? Juniors only had one midterm test for their Calculus I last year, but we are going to have three of them!

I heard professor B is planning to retire after this semester. I am afraid freshmen won't have any opportunities to take class with him.

You could also just say "third year students" and "first year students," respectively, or "the class of 2018" and "the class of 2020".

This makes your class, those students who enrolled in the fall of 2015, the sophomores, or second year students, or the class of 2019--students who have completed one year of school and are in their second year, with expected graduation after two more years (for a total of four years) in 2019.

If by "enrolled in 2014 or 2016" you mean "enrolled in the 2013/14 school year or 2015/16 school year" then the cohorts would be a year advanced, so seniors and sophomores, respectively.