Question: The Istvaeones, also called Istaevones, are mentioned as a Germanic tribal grouping in the writings of Tacitus and Pliny the Elder (~1st century AD), they categorized them as one of the nations of Germanic tribes descended from one of the sons of Mannus, the other two such peoples were the Ingvaeones and who?

Context paragraphs:
Suebi: The Suebi (or Suevi, Suavi (Jordanes, Procopius), or Suevians) was a large group of tribes who lived in Germania in the time of the Roman Empire.  They were first mentioned by Julius Caesar in connection with his battles against Ariovistus in Gaul, around 58 BC.  While Caesar treated them as one Germanic tribe within an alliance but the largest and most warlike one, later authors, such as Tacitus, Pliny the Elder and Strabo, specified that the Suevi "do not, like the Chatti or Tencteri, constitute a single nation.  They actually occupy more than half of Germania, and are divided into a number of distinct tribes under distinct names, though all generally are called Suebi".  At one time, classical ethnography had applied the name "Suevi" to so many Germanic tribes that it appeared as if, in the first centuries AD, that native name would replace the foreign name "Germans".

Aduatuci: The Aduatuci or Atuatuci were, according to Caesar, a Germanic tribe who had been allowed to settle amongst the Germanic tribes living in east Belgium.  They descended from the Cimbri and Teutones, who were tribes thought to have originated in the area of Denmark.  Much later, the Aduatuci sent troops to assist their Belgic neighbours, especially the Nervii, in the Battle of the Sabis, but were too late.  They were later defeated by the Romans after withdrawing to a fortified city.  After their defeat by Caesar they disappear from the written record, but their survivors possibly contributed to the later tribal grouping known as the Tungri in Roman imperial times.

Cherusci: The Cherusci (sometimes called the Cherusks) were a Germanic tribe that inhabited parts of the plains and forests of northwestern Germany, in the area possibly near present-day Hanover, during the 1st century BC and 1st century AD.  Ethnically, Pliny the Elder groups them with their neighbours the Suebi and Chatti, as well as the Hermunduri, as Hermiones, one of the Germanic groupings said to descend from an ancestor named Mannus.  They led an important war against the Roman Empire.  Subsequently they were probably absorbed into the tribal confederations such as the Franks and Allemanni.

Northwest Germanic: Northwest Germanic is a proposed grouping of the Germanic languages, representing the current consensus among Germanic historical linguists.  It does not challenge the late 19th-century tri-partite division of the Germanic dialects into North Germanic, West Germanic and East Germanic, but proposes additionally that North and West Germanic (i.e. all surviving Germanic languages today) remained as a subgroup after the southward migration of the East Germanic tribes, only splitting into North and West Germanic later.  Whether this subgroup constituted a unified proto-language, or simply represents a group of dialects that remained in contact and close geographical proximity, is a matter of debate.  The date by which such a grouping must have dissolved—in that innovations ceased to be shared—is also contentious, though it seems unlikely to have persisted after 500 AD, by which time the Anglo-Saxons had migrated to England and the Elbe Germanic tribes had settled in Southern Germany.

Ingaevones: The Ingaevones or North Sea Germanic peoples were a West Germanic cultural group living along the North Sea coast in the areas of Jutland, Holstein, Frisia and the Danish islands, where they had by the 1st century BCE become further differentiated to a foreigner's eye into the Frisii, Saxons, Jutes and Angles.

Sanni: The Sanni (Georgian: სანები ) are mentioned by Strabo (1st century BC/1st century AD), Pliny the Elder (1st century AD) and Arrian (2nd century AD) as a people settling near Trebizond (in today's Turkish Black Sea Region).

Rhine-Weser Germanic peoples: According to archaeological evidence, the Rhine-Weser Germanic or Weser-Rhine Germanic peoples were Germanic tribes whose settlement area in Roman times lay between the River Weser and the Middle Rhine although, later, during the Migration Period, they migrated southwest before reaching the border of the Roman Empire on the Rhine.  This relatively recent term is based on archaeological finds dating to the 1st to 4th century AD, which can be roughly divided into five or six groups and identified as Germanic.  From a comparison of archaeological evidence with ancient Roman writings, the Rhine-Weser Germanii included the Cherusci and Chatti as well as a number of smaller tribes, which are named by Roman sources and located in this region: the Usipetes, Tencteri, Sicambri, Bructeri, Chattuarii, Chamavi and Ampsivarii.  Thus, the Rhine-Weser Germanii represent the group from which the Franks came later.  The archaeological finds for the Rhine-Weser Germanii suggest they were the same tribal grouping as that referred to in the writings of Pliny the Elder and Tacitus as the Istvaeones (Istriones).

Hilleviones: The Hilleviones were a Germanic people occupying an island called "Scatinavia" in the 1st century AD, according to the Roman geographer Pliny the Elder in Naturalis Historia (Book 4, Chapter 96), written circa 77 AD.  Pliny's Scatinavia is generally believed to have referred to the Scandinavian peninsula, which in the 1st century AD had not yet been fully explored by the Romans and was therefore described as an island.  Pliny wrote that it was an island "of a magnitude as yet unascertained".  The Hilleviones lived in the only part of the island that was known, and according to Pliny, they thought of their 500 villages as a separate ("alterum") world.

Irminones: The Irminones, also referred to as Herminones or Hermiones (Ancient Greek: Ἑρμίονες ), were a group of early Germanic tribes settling in the Elbe watershed and by the 1st century AD expanding into Bavaria, Swabia and Bohemia.  Irminonic or Elbe Germanic is a conventional term grouping early West Germanic dialects ancestral to High German, which would include modern Standard German.

Istvaeones: The Istvaeones, also called Istaevones, Istriaones, Istriones, Sthraones, and Thracones, are mentioned as a Germanic tribal grouping in the writings of Tacitus and Pliny the Elder (~1st century AD).  They categorized them as one of the nations of Germanic tribes descended from one of the sons of Mannus, a Germanic ancestor.  The other two such peoples were the Ingvaeones and Irminones.

Supporting paragraphs: Istvaeones Ingaevones
Answer: Irminones