Confusing ally mechanics - me a nub

[Georodin]

Im playing with two friends in coop.
Anyway me country A and B(my friend) decided to marry our childs so were allies.
Now first I declared on a small country C war, to conquer the lower half of it. Now my B friend declared war on
the same C but the upper half of it to conquer. We thought about ourselves as allies but when we set our army's to meet at border of C our armies started killing each other.
Now I have three questions:
1. Why is the enemy of my enemy my enemy suddenly, even though were allies?
2. How can you do joint wars where you decided I take the upper half and my ally the lower half of the country? < or is the only choice to invite my ally to war? can he still do claims on territory then?
3. Was it that we met on my territory that we fought each other?


Thanks in advance

 

[jonjowett]

There should be orangey-brown icons in the diplo relation section of your character screen. (Red icons mean at war, orangey-brown means hostile.) If you hover over the icon relating to your coop partner, the tooltip might help to explain why you're hostile.

Otherwise, I think the most likely way that separate enemies can be mutually hostile is if they both declare claim wars on the same enemy for the same title. (Eg. If both your wars were holy wars then this shouldn't happen.) (The only other thing I can think of is if both of you declared war on a temporary revolt title, and the game decided to make you mutually hostile because of the interaction with that revolt title. But this doesn't fit well with your description, and I'm also not completely sure that that's what the game would do in that situation.)

In the end, maybe it'd be better to reload an earlier save and keep your armies apart...

 

[Georodin]

Im so sorry I tried to delete the posting here but did not work. Im looking for the CK3 forum actually