Act I: Inauspicious Start

Yes, Kuroi will have relayed that fact to the party, that Nevermore spotted something in the alley which posed a threat. Yes, it is possible to ready an attack. If you ready your action, however, you cannot attempt an active Perception check, nor can you attempt a Sense Motive check as it requires 1 minute of interaction with the target.

@ Jabes: Wwhen you ready an action, you only ready a standard action, so you will only have made one attack. If you wanted to make a full attack, you should've delayed instead, which will change your initiative to be after the creatures. I have no problem letting change your readied action into a delayed action instead if that is what you want... Basically: if you readied an action you can make 1 attack before the creatures reach Kayleigh's horse and shoot at them without the -4 for close combat penalty and without Point Blank Shot since you basically readied an action to shoot a creature as soon as you saw it (though you could change to shoot it as soon as it came within 30 feet) and retain your place in the initiative (since you were already right before those creatures), and if you delay, you can make a full attack at -4 because they are now in melee with Kayleigh's mount with Point Blank Shot as they are now within 30 feet of you and your initiative will change to be right after those creatures.

Here, I'll leave this here so you can check delayed and readied actions.

@Kaos: Each squares is 5 feet.

@irvanovich: Sorry, will have to wait for Jabes to pick either delay or ready before I can process your action...

Yes.

While waiting for Darren to make his save...

So, if I understood properly, each horse is supposed to take 2 squares, right ? Given that, I supposed that Kayleigh could ride till squares d12/ d13 though the marker of her horse doesn't quite fit in.

You can move through an ally's space, but you cannot end your movement in a square occupied by an ally. So you could move to e-g 10-11. Depending on how you move, you could provoke an attack of opportunity from the zombie in d11...