I'll help you through a few of these, and hopefully that will provide the support you need to more fully examine the remaining poems on your own.
"Mending Wall": In this poem, the speaker examines why he and his neighbor must rely on a physical division between their two properties. His neighbor replies that "good fences make good neighbors," and the narrator questions whether this is really true. After all, the speaker has an apple orchard and his neighbor's property is covered in pines—not cows. So what exactly are they trying to keep in—or out? The eternal dilemma that thus arises is whether physical boundaries create better relationships. His neighbor has learned this philosophy from his own father and does not question it; the belief is part of his view of the world. The question is never resolved as the narrator continues constructing a wall for which he cannot find a purpose.
"The Road Not Taken": The real eternal dilemma here lies in the title of the poem itself. While readers might be deceived along the way into thinking that the poem is about the fulfillment of taking a more difficult road in life, the speaker actually cannot forget the road that he did not take. After all, "both that morning equally lay" before him with endless potential. Although the speaker likes to envision that in his later life he will dramatically believe that he "took the road less traveled by," he cannot stop thinking about the possibilities of a different life—those he might have had on the road he didn't take. Again, he will never know how that different path might have turned out, so it's an eternal dilemma as well.
"Birches": The eternal dilemma is found in these lines:
So was I once myself a swinger of birches.
And so I dream of going back to be.
It's when I'm weary of considerations,
And life is too much like a pathless wood
The carefree world of childhood beckons the speaker through memories of his own boyhood days when he spent unstructured time swinging in birch trees. In adulthood, he longs for these carefree days when his life becomes overwhelming in its demands and confusing in its choices. Of course, there is no real way to return to the days when he "climb[ed] black branches up a snow-white trunk / Toward heaven," so he is left with an eternal longing for a world that no longer exists for him.
"Stopping by Woods on a Snowy Evening": This is a poem of opposite attitudes. The scene the speaker describes is one of both serenity and an ominous sense of danger. On one hand, the snow is "lovely," yet the woods are also "dark." Although the speaker longs to stay for a moment to feel the peace of a snow-filled forest, he also doesn't want to be caught by the man who owns the property. The horse feels that this might be a "mistake," and all of this happens on the "darkest evening of the year." This isn't just a peaceful scene of a traveler admiring nature; there is also an undercurrent of secrets and darkness that weaves itself through the poem.
I hope this gives you a good start as you consider the other poems. Good luck!