It seems, I've solved the problem with the Ember Dinovaldo DLC.
Used in the second time the DLC Quest with Kechawacha, Blangonga and Rajang, because there are multiple monster in that quest.
Now I've created a quest with Ferocious Lagiacrus and Tamamitsune at the same time, than a White Gale Nargacuga will spawn, after the Nargacuga is dead, an Ember Blade Dinovaldo will spawn and at least the Amatsumagatsuchi spawn. I've wondering that the Amatsumagatsuchi can spawn in the Dragon Graveyard. He will turn the Area into a wonderfull blue light, when he goes into phase 2 like the hydra does, when it is outrage lol.
The Quest works, all 5 Monster spawn and if i slayed the Amatsu the quest was clear.
Some notes:
-To make a monster spawn into the quest you have to change the Boss spawn number when you edit the bosses (you can get the ID of your boss when you look into the Quest data page and count up to your Boss Name)
Important: The field "none" has to be count at 1 not 0 the first boss monster has the ID 2
-Hardcore variant Monster will crash the game if you try to make it to an Ferocious Monster
-If you add Bosses to the quest (mine include 5 bosses, not 3 as the original quest) you have to add an 6. monster line with nothing in it.
In the pictures you can see which IDs I mean and where you find your Monster ID
If you don't change the original ID, the monster will never spawn in the quest