So I was randomly thinking about what Father's motive is in creating the Homunculi and doing all this stuff. And also what the deal is with the whole "human sacrifice candidates." And I've come up with something...
In Chapter 49, Marco thought that they're trying to turn the country into a giant transmutation circle to make a Philosopher's Stone. Envy says he was close, and "heading in the right direction."
And in Chapter 51, we find out that Gluttony is a failed attempt to create the Doors of Truth. Father is obviously very interested in the Doors of Truth for some reason. In fact, it's remarkable that he even knows about it's existance, unless he's seen it for himself.
We know that all the candidates for human sacrifice mentioned by the Homunculi are very talented alchemists (the Elric brothers, Roy Mustang, Tim Marco, Izumi Curtis...).
We also know that so far, the only way to enter the Doors of Truth is by giving a passage fee, a sacrifice of some kind. It may be an arm, a leg, an eye, internal organs, or even an entire body. But the fee is expensive. And so far, the only way we've seen people get to that point is via human transmutation, with a transmutation circle.
My theory is that the Homunculi are making a giant transmutation circle, but not to create the Philosopher's Stone. (I mean come on, why would they need the Stone, the Homunculi each have one already!) Nor is it for human transmutation. The purpose of this circle is to get to the Doors of Truth. But who will pay the passage fee? Why, the human sacrifices!
Probably only the best alchemists would be able activate such a giant circle, and even then it may take more than one person at the same time. It would also be wise to find alchemists who have already seen the Doors of Truth once and survived (Ed more than fits the bill, since he's been there twice).
So yes, even if in the end they are all sacrificed, it'd be absolutely necessary that you keep them alive and healthy. Losing just one would be a major setback to the whole plan. As for how they'll convince the alchemists to do this, maybe they'll use force, hold hostages, make threats...
So going by this theory, Ed and Al were right in going after the Homunculi for information. And if Al meets Father in the coming chapters, they may get all the information that they were looking for. Father is practically running the country, and he's apparently an expert on the subject.
But then where would that leave them? They'd be trying to do the same thing as Father. Would they go along with his plans, or come up with an alternative solution? They'd probably go with the latter, because they've vowed to move forward without getting anyone else involved. How they'll do this, no one knows. But they're geniuses and are determined enough to figure something out, and maybe in the process help Roy get the country back together by spoiling Father's plans.
And that's where my speculation ends.
EDIT: Also linking my Wrath theory so I can keep track of these better.
EDIT: Look! Support for my theory!