How best to approach a siege?

[ccvtp]

So I am relatively inexperienced in Imperator Rome. I want to attack a neighbor to the west , but his capital buds right up to my border and the capital of his ally is right above his capital. To the south however is an unfortified enemy province. My problem is that I have an ally to the west of the enemy and I’m afraid that he will just take all the unfortified territories for himself and doesn’t hand them over.
But if I rush past the capital of my enemies, I’ll be right open for them to siege me down. I have another ally right to the north of me. If I only call him in I won’t have to fear my western ally to take the land in the west, but me and my enemies would have exactly the same troop count.
I could also just hire mercs to replace my ally in the west, but I would like to save that money if I can avoid it.

Any advice? Thanks so much guys.

[Feynrik]

The key i follow in all wars is never split up my armies to carpet seige before enemy head armies are crushed.
Misuse your allies sources and armies scroupleless !
Play safe but aggressive and win.

[Bunny Juice]

One straight tip: pre-position troops and declare war on the 1st of the month. Enemy AI's garrisons are at 1/4 when they're peace, and refill by a few 100 each tick (month) when at war.
Agreed with the other reply, in a fairly equal-sized showdown first prio should be wiping the enemy army, preferably on their own capital during the first month of the war so you can start a 250-man siege.
You could also hire the mercs and position them before declaring if you decide the southern region mentioned is worth it (disband mercs is quick and easy, so it could be..) At least they can wipe out/disperse the enemy main army (likely a small 2k) and securing the occupation right away before the ally arrives.
Also agreeing with the above, at any point if allies are willing to join, call them in no questions and misuse them to no end; it's not Crusader Kings where you actually owe them favours after, so unscrupulous is the way to go here; heck I'd even start fabricating CBs on them during the war without an afterthought. For any non-major tag, at start date you can usually consider yourself spoiled if you're able to raise more than 2k troops, so that first war is usually make-or-break. I'm not saying you should systematically declare on a tag on Nov 1 the first year, I'm just saying that's what you'll end up doing inexorably in your time with IR XD.
Now, I never did multiplayer, but I can only imagine doing any of the above unannounced in MP is prone to terminating a friendship or two. ^.^'

[HACKFRESSE]

I use mercanaries with storm attacks. they are expensive and not very loyal.
then I disband them soon.
it is a fast way to control the other territorities.
and why lossing thousands of your own reserve ?
;)