The rules on the KMT sheet state: “An attack by a foreign country on a Warlord, CCP, or KMT, is considered an attack on all of China and causes all Warlords to Align with KMT. If a warlord is attacked by either Chinese faction, it and all its remaining land zones and units align to the other Chinese faction if unconquered by the end of the Combat Phase.”
So to answer your questions
What happens if the CCP attacks a Chinese Warlord (are they allowed to attack warlords?)? Is it correct if they attack one warlord that all warlords go to KMT?
No, an attack on a warlord by CCP/KMT causes the attacked warlord to align with the other Chinese power; Other warlords remain neutral. Remember aligning occurs after combat is resolved so only that warlord’s remaining unconquered land zones and units go to the other faction.
What happens if the KMT attacks the warlords. Do all of them become CCP?
Same as above, only the attacked warlord goes CCP at the end of the round if they have territory remaining.
What happens to the warlords if the CCP attack the KMT and vice versa?
Nothing, they dont care.
Am I correct to assume that all Warlords become KMT if Japan attacks KMT?
Yes. And keep in mind RAW states “Attacks” not declares war on. This means Japan could DOW KMT and just blockade them and not align all warlords. It also means that KMT can freely attack Japan and Japan being unable to counterattack without aligning the remaining warlords to the KMT.
What happens to CCP if Japan Attacks KMT or one of the Warlords?
They can sign a truce with the KMT if they wish. IMO they should do so, and if they dont have a border with the USSR yet, move units to a KMT region next to the boarder and then break the truce to get Lend Lease and their wartime bonus income.
Hope you enjoy your game!