Re: TT-model Passenger sleeping coach

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Well, may be, it would be interesting to know what's behind a name. But even if I possibly try to understand the meaning, I'm not going to use a translated name.
...because it stays a name—the train's name.

My buddy Fred doesn't like to be called Fritz (same name—other language). And my neighbor here in Dresden (his name is Sascha [German spelling of Sasha]) will not even feel addressed if I call him Alex (same name—other language).
To use the translation of a name is a sign of a lack of respect in my eyes—indifferent if it's about a person or a thing.
So, if a train's name is Омич (Omich), I will call it Omich and not Omsker.

It's simply a question of respect in my eyes.

By the way:
Юность is one of the few Russian words which I understand without dictionary.
... besides вокзал, of couse—the most important word in all languages.

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What was VEB Kombinat Schinenfahrzeugbau DDR? The exporter?

It was the trust owning all manufacturers of railroad vehicles in GDR—kind of holding company.
It was founded in 1945 and initially named "VVB des Lokomotiv- und Waggonbaus" (Association of People's Own Companies of the Locomotive and Carriage Building)—abbreviated: LOWA. In 1954 it was renamed into "VVB Schienenfahrzeugbau" (Association of People's Own Companies Rail Vehicle Building). Later it got its final name "VEB Kombinat Schienenfahrzeugbau der DDR" (People's Own Company Corporation Rail Vehicle Building of the GDR). Following companies were owned by it:

• VEB Waggonbau Ammendorf (responsible for providing Soviet Union with sleeping cars—for instance those which this thread is about)
• VEB Lokomotivbau "Karl Marx" Babelsberg—official abbreviation: LB; colloquially usually abbreviated: LKM (only manufacturer of steam locomotives in GDR, additionally all kinds of diesel locomotives; last locomotive made in 1976; from 1969 on manufacturing of refrigerating devices and cranes and so on)
• VEB Waggonbau Bautzen—official abbreviation: WB (manufacturer of passenger cars, mainly coaches, combined coaches with baggage compartments, couchette coaches and diesel railbusses and also few sleepers; from 1960 on additionally manufacturing of television aerials and camping trailers)
• VEB Waggonbau Dessau—official abbreviation: WBD (manufacturer of freight cars, mainly reefers; additionally manufactured: handcarts, bicycle trailers, wooden window frames and doors and so on)
• VEB Waggonbau Gotha (only manufacturer of streetcars [trams] in GDR, additionally manufacturer of freight cars [mainly hoppers, reefers and heavy weight and depressed center flat cars] and during early 1950'ies also glider planes; last streetcar made in 1967; from 1967 on change of production into manufacturing of extractor fans, refrigerating and water treatment devices, from 1983 on also chassis for autos)
• VEB Waggonbau Görlitz—official abbreviation: WG or GöWa (GDR's passenger car specialist, mainly double-decker cars and train sets, but also railbusses and MOW railcars, DMU's, dining cars, sleeping cars, RPO's and baggage cars and all kinds of special cars [for instance Pullman carriages and associated cars for several governments], also few coaches and couchette coaches)
• VEB Lokomotivbau Elektrotechnische Werke "Hans Beimler" Hennigsdorf—official abbreviation: LEW (last locomotive manufacturer in GDR, mainly manufactured EMU's for Berlin S-Bahn [suburban railroad] and U-Bahn [underground railroad] and electric locomotives, but also diesel locomotives)
  LEW furtherly owned following companies:
  • VEB Schichtpreßstoffwerk—official abbreviation: SPW (laminates)
  • VEB Galvanotechnik Leipzig—official abbreviation: GTL (galvanizing technology)
  • VEB Industrieofen- und Anlagenbau Güntersberge (industrial heaters and various equipments)
  • VEB Infrarot Anlagenbau Oranienburg (infrared equipment)
  • VEB Schaltgerätewerk Werder (switching equipment)
  • VEB Schaltgerätewerk Muskau (switching equipment)
• VEB Waggonbau Niesky (manufacturer of various kinds of freight cars and trucks [bogies] for freight cars)
• VEB Waggonbau Werdau (various railroad cars; already 1952 outsourced from LOWA, change of name into "VEB Kraftfahrzeugwerk 'Ernst Grube' Werdau" and change of production into manufacturing of busses, trolley busses, bus trailers, road trucks and trailers and bodywork for trucks)
• VEB Schwermaschinenbau "Heinrich Rau" Wildau (initially manufacturer of parts for locomotives and little industrial locomotives; from 1950 on manufacturing of crankshafts for ship's diesel engines, bearings, machines for pipe production and so on; eventually outsourced from VEB Kombinat Schienenfahrzeugbau der DDR)
• VEB Waggonausrüstungen Vetschau (manufacturer of trucks [bogies] for cars, mainly for passenger cars; most trucks made there had been developed by VEB Waggonbau Görlitz)
• VEB Federnwerk Zittau (manufacturer of springs)

What is/was DEWAG?

It's the abbreviation of "Deutsche Werbe- und Anzeigengesellschaft" (German Advertisement and Announcement Company).
It was the national agency responsible for all kinds of public relations. It was owned by "Sozialistische Einheitspartei Deutschlands" (Socialist Unity Party of Germany)—abbreviated: SED—which was the largest and most influential political party in GDR.

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Except for the last one, they show Ammendorf-type cars.

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Here 2nd, 4th and 5th pictures show Ammendorf-sleepers.