Books in a trilogy are significantly different lengths. What to do?

I’ve managed to write a fantasy book, Lord of the Rings-style. That is, a single story that would almost certainly be published as three separate books with multiple branching plotlines. Or at least, I’ve written the rough draft of one. Having more-or-less completed the rough draft, however, I’ve noticed a potential problem. My books are of dramatically different lengths. In particular, my first book is much longer than my second and almost twice the size of my third.

The way I see it, I have seven options:

1) Polish up the story as-is, and hope a publisher/agent will accept a large debut novel (strike one) that doesn’t stand on its own (strike two) from an unknown author (strike three). This still doesn’t address the issue of the different book sizes, which I imagine might be annoying for a reader.

2) Split the first book into two smaller books. This makes all the books about the same size, but I’m not sure I can have good “stopping points” for the plot threads between books 1 and 2 if I do this. Maybe with enough rewriting.

3) Split the story into two parallel stories. Of my three-and-a-half or so plots, my A and B plots are more closely aligned, as are my C and D plots. There isn’t much (direct) interaction between the two stories, though both are reacting to the same outside events, and the events of one story does have some indirect effects on the other story; without this knowledge, some events might seem to be happening “out of the blue”. Rewriting could probably fix this, though I’m not sure the overall…theme, for lack of a better word, could be maintained without all four endings.

4) Cut, cut, cut from Book 1. Maybe a subplot or two could be removed. Perhaps Plot D could be cut in its entirety (I’ve thought about cutting it anyway, since it isn’t vital and is rather darker than the rest of the story, but I’ve held off thus far because of thematic consequences to removing it). But trying to cut out half the book seems…ambitious.

5) Further flesh out Books 2 and 3. Adding a subplot to Plot B could be a relatively easy and effective way to fill out Book 2 (I’ve thought about doing this as well, as Plot B is somewhat anemic in Book 2); and perhaps some more details in Plot C would be good in Book 3, though perhaps that would simply be a distraction.

6) Merge Books 2 and 3 into one. I’m not sure I can do this easily, since there’s a bit of a time-skip between Books 2 and 3 and the climax of Plot B really wants to go at the end of a book. Still, perhaps fixable with serious rewriting. This still leaves Book 1 fairly long, and I suspect that from a publisher’s perspective a trilogy is a more attractive proposition (i.e., more potential sales) than a duology.

7) Shelve the story for now. Write another book, try to get it published and make a name for myself. This might help get Book 1 published as-is, though the dramatically different book sizes would still be an issue. Plus, my next book will probably be science fiction, not quite hard science fiction but close, and a rather different style as well.

I’d like advice on what to do, of course, but I’d also like advice on how to decide what to do. I’ve been stuck here for almost two months, unsure what to do. Each option requires a significant investment of time and effort, so there’s a huge incentive to get it right the first time.

Any advice would be greatly appreciated.

Addendum: Thus far I’ve tried to keep the question fairly story-agnostic, in the hopes that a good answer will help in more than just my particular circumstances. Since the details of my work might affect the answer, however, I include a brief summary below, with approximate word counts.

Before giving the breakdown of my plotlines, let me note one important point. Where Lord of the Rings has the characters start out together in the first book and then break apart into separate storylines in the second and third books, I go the reverse direction: characters start out separately in the first book and come together as the story progresses.

Okay, so here’s the breakdown:

Book 1 (255k words):

Plot A – 65k words

Plot B – 64k words

Plot C – 87k words

Plot D – 38k words

In this book, all plot threads are effectively independent. Mostly the characters are reacting to common events over which they have no direct control (an assassination for Plots A and B and an invasion for Plots C and D). Plot A ends on a cliffhanger, Plot B reaches a significant milestone, Plot C is ongoing and Plot D attains its climax.

Book 2 (144k words):

Plot A – 77k words

Plot B – 7k words

Plot C – 53k words

Other – 7k words

In this book, Plots A and B get loosely merged into one combined plot, which is part of the reason that Plot B gets so few words, though B doesn’t get much play in this book anyway. Plot C is still separate, and “Other” is just a character bridging over from Plot C to Plot B. Plot A ends on a semi-cliffhanger, Plot B gets no real conclusion at all, and Plot C reaches its climax.

Book 3 (128k words):

Plot A – 66k words

Plot B – 24k words

Plot C – 39k words

Here Plots A and B reach their respective climaxes, while Plot C is mostly a long denouement with a bit of interplay with Plot A. Some rewriting could alter the amount of interaction that Plot C has with Plots A and B.