So Im running a campaign where one of the encounters has a sentient construct that controls 12 flying swords. The information I read to my players say that the 12 swords seems to act as one. What I'm trying to figure out is if I should run it as 1 "creature" where all 12 make a single attack or give each sword its own attack round. And, if they re all to make a single attack in one round would I take the stats and damage for just 1 or all 12. This should be a CR 5 for 4-7 at APL 4.

Thanks in advance for any suggestions or advice.

You can give the creature different attack modes. One would be to attack a target with all swords at once (one attack roll). Another option would be to attack several targets with a few swords each (many attack rolls). Yet another choice would be to attack with some swords and have some defend, increasing the creature's AC.

One thing you might want to consider is having the creature lose control of swords as it takes damage. So when it loses 1/10 of its HP, it loses a sword.

You could always just borrow from Animate Objects.

You could borrow the hundred-handed whirlwind from this:

https://www.d20pfsrd.com/bestiary/monster-listings/outsiders/titan/titan-hekatonkheires

Basically give your monster multi-attack (2-3 attacks) and the attacks hit all creatures in range simultaneously.

If the players somehow destroy 1/3 (1/2) of the swords reduce the number of multiattacks.

At level 5, I’d think it would just be one attack. Just from an action economy standpoint, that’s a lot of attacks for the bad guy. Unless it’s a solo/boss type. Then that could actually work, where the swords stand in for the low level minions that might normally be in the fight. So if a solo, then let them attack individually, if there’s other creatures, not. 
And I’m guessing there’s rules for if the player want to target each sword to reduce the number of attacks, or just focus on the main body and end it all at once. 

A few different options come to mind:

1. "Cloud of Daggers / Moonbeam":  The flying swords are an area of effect spell. Anyone who starts their turn or moves through the area takes damage.  You could add a saving throw to the effect.  Narrate it like the swords are attacking, but use the Cloud of Daggers/Moonbeam mechanic.  Adjust damage as appropriate.
2. Swarm:  Inspired by Naresea's comment.  Treat the flying swords as a swarm monster.  Medium/Large/Gargantuan based on how much space you want the swords to threaten.  When the swarm takes more than half damage the threat is reduced.  Swarm of Rats
3. As mentioned above, treat them as one of the monster's attacks.  The flavor reminds me of the Batari Battle Stacks from the Tomb of Annihilation campaign book.  Basically, one (or more) attack while the others take the "Help" action.  Have the flying swords make one (or more) attacks with advantage.  At-will advantage attacks are going to be devastating to your PC's so either use this option sparingly, or provide a method to avoid/block the attacks.  Even low damage attacks are going to add up quickly.

Hopefully the links work correctly.  First time trying that.  I tried to pick basic rules options so they would be viewable by everybody.

Note: you could combine some of these effects if you are up to the challenge of running a mechanic intense fight.  For example, the flying swords are treated like option 1 until commanded by the boss (via action/lair action) to perform as option 2 or 3.  Option 2 would be fun if they were commanded to "hunt down" a PC.  Give the swarm a movement such that the PC has a decent change to "run-away"/avoid them. (Are you familiar with the concept of Kiting in online games?  keeping a monster just of reach to keep it from harming your friends.)

Thanks for all the suggestions everyone.