Alright let me try to shed some light on a few things you mentioned. First, the King's Guard is a NEUTRAL FACTION, meaning they do not belong to the Westerlands, they belong to the King of the Iron Throne. This is a feature that Produno has been trying to figure out for a considerable amount of time, it is very complicated, it improves with every mod version, and I appreciate his efforts to try to create this feature. It will eventually be fully developed. Are you using the Steam or Mod DB 2.2?
I assume this is an issue for you because you want to recruit them to your banner. Let me explain away to do that and it has been successful for me during my play through. First, you need to make friends with Joffery, I know many hate this idea, but it makes the treachery we are about to embark on even sweeter...
Convenience Joffery to attack deep into the Stormlands, because you want his army annihilated and the Kings Guard to be captured. You want to be a mercenary or a vassal of the Westerlands when you do this since you will need to be able to attack the Stormlands. After Joffery is defeated, you will want to attack the armies in the field with the Kings Guard as prisoners. (note: this fails if you rescue them by taking a castle) Once you destroy the Stormlands army with them as prisoners, you will get a dialogue option to recruit them to your cause. They will not all accept this kind offer, but some will. You will have to repeat this process up to 8 or even 9 times. You will lose relations with Joffery every time he gets annihilated on your "suggestion" but this can be negated if he does the suicide run on his own or if you rescue him from captivity. You can not initiate this process if you are the attacker of Joffery, because you are assaulting the king when you attack (Note: You can not be an enemy of Westerlands though Joffery can dislike you), it has to be strictly rescue. The King's Guard will become companions that you can equip, level up, but they will not be able to become lords.