I've read from some sources that you may bluff the Transcendent One that his Shadows are rampaging to buy you time to resurrect your party members.

How do you do this, and do you get to resurrect ALL your friends for a final showdown?

I have heard that you can resurrect two allies, I dont know how to do this. However, why would you want to do this? the fight is very easy without resurrecting anyone and you dont have to fight anyways. It is a much better endig if you merge with the Trancendant One.

You can tell him that through one of the dialogue options...

(MAJOR SPOILER)

And yes, you'll have enough time to resurrect all of your companions and they will help you kill the Transcendant One. After that is done, the Nameless One will have one last conversation with each of the party members before he goes back to fight in the Blood War. This is probably the best option to pick for the final fight, you get to see the most. Of course, you can replay the ending 5 times and use all the different options too...

Resurrecting two party members involves first asking the transcendent one to revive your party, and he'll refuse. Challenge his abilities and he'll tell you about his power over life and death, and you'll remember that you'll have it too.

Now I haven't tested this yet, but Morte wasn't really dead, he was just feigning. Choose him first, then choose the other NPC of your choice.

Tal, I tried looking for that dialogue option but couldn't find it. I chose the above mentioned tree first because I thought remembering would help, but later the options didn't seem to change. What do I need to do exactly?

Hmm, maybe it depends on a stat like charisma... I don't remember having to do anything special, just navigate through the dialogue tree very well since there are a lot of paths you can take.

By reading your text I suspect that Deionarra hasn't told you that you have the power to bring your companions back from death... Interesting. You can learn this very early in the game (in the Mortuary) and it comes in handly quite often during the game. I've never heard of anyone learning it so late in the game. ;)

I could revive all of my companions without any trouble while the TO was gone IIRC. But then again, I had very high stats, I was very high in levels and I knew a bit more about myself from the beginning. Maybe that's your problem here...

The endings I've managed to get are (most done through dialogue options)
1) Merge with the TO
Do this by either getting him to say your name and then forcing him to merge or by threatening to kill yourself with the Blade of the Immortal
2) Kill yourself
Like the above but instead of merging use your will to unmake yourself or just stab yourself with the blade of the immotal
3) Kill the TO
This is done in a number of ways.
1) Tell him that his shadows are running amock and he'll go check it out. This allows you to ressurect your whole party and when he comes back you can just kill him.
2) Get him to allow you to ressurect some party members. He'll only allow you to ressurect 1 but if you choose Morte first it turns out he isn't dead so you can ressurect another. You can choose anyone but I prefer to pick Dhakkon or Vhailor since they both get substantial power up when they get up, making it that much easier to kill the mofo.

I've done all of the above but personally I prefer merging with the TO.