[Kalimac]

I'd agree that Elfhelm knew who Dernhelm really was, if nothing else on the basis of the "understanding" they seemed to have. I'm not sure that it's really evidence that he had an unrequited love for her, though - in fact, if he were romantically in love with her, he'd probably be *less* willing to let her go into a situation where (as he would think) she had a 99% chance of being killed. If he felt more brotherly towards her, though, he might be swayed by her pleas that she's been training for this sort of thing her whole life, why can't she use it in her peoples' defense, like everyone else? Also, there is the matter that while their force was nice, it was not overwhelmingly enormous, and every extra rider would help.

It's true that she has sworn to Theoden to stay behind with the citizenry, and by allowing her to come along, Elfhelm is essentially abetting her in breaking her oath. But considering their situation - they're only expecting to survive a matter of days. (What were the odds that the Ring would really go into the fire, anyway? Elfhelm didn't know these particulars, but surely that black cloud from the East couldn't have been encouraging). His thinking may have been along the lines of "In the end, we're all dead. Might as well go out with a bang."

As for Dernhelm's dispute with Elfhelm, I'd guess it was over Merry. While Elfhelm might understand the reasons that Dernhelm could be good in a fight, he hasn't seen anything to indicate that Merry has any particular skill at all that would prevent him being slaughtered in the first five minutes. While he may be expecting that none of them will live very long, I doubt he'd want Merry to throw his life away without effect like that.

So Elfhelm probably knew, but the other riders probably didn't. For one thing, had they known, they would probably have tried to hover around Eowyn a little more than they did - protecting the woman, and all that, even if subconsciously. She would have been a lot more hampered in her movements at the beginning of the battle. And when they saw Merry riding with the new boy, they probably figured that Merry had pleaded his way in with Elfhelm somehow, so who were they to dispute? Besides, the boy would be lighter than any of them, and so better able to bear the extra weight on his horse.