Translation:The youth of today does not sleep in the morning.
"por la manana" or "en la manana" means "in the morning, since "la manana" = morning. "el manana" as a noun means, loosely, the future. In Mexico, if a shop owner tells you he'll have it "manana," it pretty much means "not now, maybe someday, good luck." As an adverb "manana" means tomorrow. "manana por la manana" = tomorrow morning, "manana por la tarde" = tomorrow afternoon
I disagree depending on the usage. Although the troop IS crossing the bridge I am referring to an unit. The troop is a group of people, and you can have troops, which is clearly plural in Spanish or English. So the troop of people ARE crossing the bridge and the troops ARE crossing the bridge are both correct, but have different meanings. This is different as "youth" is not a unit or an individual and should have been plural in Spanish to make sense (otherwise there is only one young person today). As used in the English translation it is plural. Let me modify it a little for clarification. The youth ARE sleeping. This is the same collective (but not unit) youth used in their English translation. If you read "La juventud es duerme" you would correctly translate it as "The youth IS sleeping" here the youth is clearly singular and matches the Spanish. Additionally, many English speakers will say "The youths ARE sleeping" if referring to either a specific group of children or (although it is contrived) all children.
Unless I have missed or misunderstood some special or particular point that you're making, "The troop of people are crossing the bridge" is not a grammatically valid sentence in English. The noun in the sentence is 'troop,' which is singular, even though it likely refers to a collection of multiple individuals. The 'of people' part is just a prepositions phase. While it may be important to the meaning of the sentence (perhaps to distinguish between the bridge-crossers and the troop of monkeys crossing on the river rocks), the prepositional phase does not change the conjugations of the verb. One must say "The troop of people is crossing the bridge."
In English, "youth" can refer to either the collective young people of the contextual world, or to an individual young person, so there may be a bit of confusion there, but here we are definitely using the collective noun, and collective nouns function as above.
Whether a word is a collective noun in one language and/or it's translation in another depends on the language. We may say the youth and use it as singular or plural depending on intent, but en español, la juventud is a singular collective noun so of course it would match that. Just because we can make it "the youths" doesn't mean they are obliged to go with las juventudes so it becomes a direct translation to the english. We need to learn what they would say.
Also, your sample sentence should read "la juventud duerme", no "es."