As much as I know, only Nachzehrers are allied with Wiedergangers, but all other factions are hostile to each other. Don’t take me for word on it however.
That of course changes during greenskin and undead invasions when Goblins/Orcs or Wiedergangers/Ancients unite.
There might be exceptions in certain quests, for example when you encounter thugs meeting necromancer.
I am not aware of Direwolves being allied to anybody. However Direwolves are one faction which you absolutely don’t want to have in the multi side fight. The purpose of those fights is to let others fight while you wait it out, then finish what remains. This means that you want to retreat at the beginning of the battle in a way that will lead two enemy groups in to each other. Or most of them at last. Problem with Direvolves is that they have high initiative and lot of AP and many of them will reach your line at the beginning of the first turn, thus not letting you to retreat. Same is true for Goblin wolfriders. So avoid combining fights with these.
But otherwise I have lot of good experience with making two enemy groups fight out. I was able to clear locations which would have being impossible otherwise.
As for gheists:
You need sergeant with about 100 resolve.
Your front line should have 45-50 resolve or more.
Your backline should have about 40 resolve at last.
Effect of standard and rally ability depends on range, so you want to essentially turtle around your sergeant. Don’t spread out.
Having second sergeant is not essential but can be very useful.
You should select dedicated guy with high melee attack and give him spear to serve as a gheist killer. Give him undead necklace if you have it already. If not, get it asap.
If you don’t have those things, don’t bother to fight gheists. They’ll destroy you.