[Boromir88]

Well, three elves is not quite support... if I'm not mistaken, some American soldiers (or was it airplane pilots) fought in WWII before the US joined the war, yet it does not indicate that the US was supporting his allies in a militaristic way.

But unlike the WWII scenario Elladan and Elrohir were actually sent by Elrond. And the Dunedain were summoned by Galadriel and told that Aragorn needed them. So, though the Elves couldn't march out in force (since their kingdoms were being attacked) they still did what they could. Even if it be only two elves, and thirty Dunedain, they will still sent to aid Aragorn by Elrond and Galadriel. Just showing we got your back, so to say.

As far as the Generals/armies thing. Yes, in ancient times the name of a General or King also includes their army. For instance in the Crusades, often it is just "King Lionheart versus Saladin" and the only names as mentioned, but of course it includes their armies. And as Nogrod says, Shakespeare typically did the same. But, it's not a style, as far as I've seen Tolkien used. When naming a General/Commander, Tolkien always gives us atleast an approximated number of their men. As far as I'm aware of that is. Let's take for instance when the outlying lords are coming into Minas Tirith:

"Forlong!" men shouted. "True heart, true friend! Forlong!" But when the men of Lossarnach had passed they muttered: "So few! Two hundreds, what are they? We hoped for ten times the number..."

And so the companies came and were hailed and cheered and passed through the Gate, men of the outlands marching to defend the City of Gondor in a dark hour; but always too few, always less than hope looked for or need asked. The men of Ringlo Vale behind the son of their lord, Dervorin string on foot: three hundreds. From the uplands of Morthond, the great Blackroot Vale, tall Duinhir with his sons, Duilin and Derufin, and five hundred bow-men. From the Anfalas, the Langstrand far away, a long line of men of many sorts, hunters and herdsmen and men of little villages, scantily equipped save for the household of Golasgil their lord. From Lamedon, a few grim hillmen without a captain Fisher-folk of the Eithir some hundred or more spared from the ships. Hirluin the Far of the Green Hills from Pinnath Gelin with three hundreds of gallant green-clad men. And last and proudest, Imrahil, Prince of Dol Amroth, kinsman of the Lord, with gilded banners bearing his token of the Ship and the Silver Swan, and a company of knights in full harness riding grey horses; and behind them seven hundreds of men at arms, tall as lords, grey-eyed, dark-haired, singing as they came.

If you look through the Last Alliance and The Black Gate Opens, you will see the same kind of thing. Tolkien may not give an exact number, but his style is different from the typical history. When he names a General he gives some sort of approximated number, or something to give us a idea of how many (few for instance). With that said, I don't see a reason to assume it's different with Elladan, Elrohir, or the Dunedain. If they are named with no number/approximated guess, then I assume they are by themselves.