There's a god involved then. Fuckitfuck.
Anyway, probe her more. And STALL!
Let's go with something of the such:
"You ask as if you can't simply rip it out of my head.", "You ask as if you needed me to tell you that.", "You entered my head, can't you simply see it?" or something of the like. Overestimating their capabilities is nice and their reaction to implying that they could know it without us telling him might tell quite a bit about what is the actual limit to their powers.
Probe her on the "the only one now, really." part as well. The only one,
now? Were there more?
We also have no evidence but her word that she really there on behalf of Morka, which we also only have her word as evidence that he is indeed a death god. She isn't outright hostile to our paranoia, so this probably won't really cause offense.
But anyway, their goals are pretty clearly evil. They want to conquer the world, kill all those who oppose and possibly some more (necromancers... They just need a viable breeding population to keep them supplied with raw materials). They try to dress their stated goal as creating a safe world, but the real stated objective is to conquer the world, and put the necromancers in power, period. We also don't know if she will actually share power or just use us as dragon and/or cross us the moment we are not useful to her anymore. Outright refusing and being hostile is probably unhealthy. Stall. STALL! Stall until you grow old and gray (yes, you are an elf, that will take a long time, so?
). Show reluctance. Don't be outright hostile, do
not do the whole swearing you will never join then, etc. Basically do not burn any bridges. While, yes, we do not intend to ever cross them the time they expend courting and trying to convert us is time they don't spend trying to hunt and kill us. And
that is something to worry about.
There are very few necromancers, and each apparently is a incredibly useful and grand resource. They are unlikely to give up on recruiting us even if we don't join up immediately, but that changes if we are apparently directing opposing them and do not show signs of changing our mind. So, STALL! Ask for time. Show reluctance. Ask to be given the opportunity to see more of the world with your own eyes first and confirm there's no chance of peaceful existence (framing it something like: "Let me see by myself that my "foolish naive dreams" are indeed foolish naive dreams."). Stall, stall, stall. Stall until strange aeons come and death itself dies. STALLLLLLLLLLLLLLLLLLLLLLLLL!
If they absolutely corner us and force a decision
now, without any possibility to avoid it, we can see what possibilities we have in hand, but I'd say put a price for our help: Namely, leaving the elven lands alone. Not even if the elf attack the necromancers they should be attacked on their lands. Elves outside them might either be fair game or protected unless they attack first, but either way, the elven lands should be safe. Still, don't make the decision unless we absolutely have no other option. Instead, stall, stall, stall!
Anyway, on the morning inform Omo of the situation, and tell him you need to start working on becoming able to oppose them, which including training, researching and building a power base. Work on doing so. We need to work on overtime to be able to be in a position where we can actually declare opposition to the other necromancers. If the necromancers can somehow scry us and see that we tell them that we are doing so so can keep him as our asset for now and that we are working on creating a power base so we are safe from those who would hunt us. Stall some more. Also, research old tomes and etc. to discover if there is any "good" death god, or at least a neutral one. We might need a god to handle another.
If the necromancers start to actively hunt us and seems to manage to know where we are, run back to the elven lands. The council can probably use this information. And yes, reveal ourselves to them. Put ourselves as a possible weapon against the others and pray that they don't decide to kill us them. Try to get our mother, father, mentor and ex-girlfriend in our side before actually revealing everything of course.
Oh, and have I mentioned that we should stall? At the very least put it to the shock and ask for time.