[quote=@Turboshitter]
I has a question. We can use Servants from Fate/Grand Order, right?
[/quote]

No, you cannot. I'm sorry if this kills your hopes, but much of what we know of Grand Order is incomplete, and what we do no may not be fully understood. Additionally, the Grail System of Fate/Grand Order is inherently incompatible with the traditional Grail System, so many of the Servants from there will likely be incompatible with the world of this one.

I will say that you may be allowed to app your own take on a Heroic Spirit named in Grand Order, however. J-Just don't use their "canon" versions, okay?