The swashbuckler's Opportune Parry and Riposte states that the only important requirement for activation is,
...when an opponent makes a melee attack against the swashbuckler...
Using no language that bars attempts against attacks made at reach. However, it does state that while the swashbuckler can parry such an attack, the riposte portion of the ability can only be used
...provided that creature is within her reach.
Clearly preventing retaliation if the swashbuckler themselves cannot reach the creature that attacked them.
Isamu cannot use Opportune Parry and Riposte with any attack that is not directed towards him. He can, however, use his standard action to Aid Another against an attack directed against Lily. This is an attack roll made against an AC of 10. He would need to ready the action, since he cannot Aid Another while an attacker isn't within range. Additionally, the attacker must be within Isamu's own attack reach in order to activate the Aid Another readied action.
In melee combat, you can help a friend attack or defend by distracting or interfering with an opponent. If you’re in position to make a melee attack on an opponent that is engaging a friend in melee combat, you can attempt to aid your friend as a standard action. You make an attack roll against AC 10. If you succeed, your friend gains either a +2 bonus on his next attack roll against that opponent or a +2 bonus to AC against that opponent’s next attack (your choice), as long as that attack comes before the beginning of your next turn. Multiple characters can aid the same friend, and similar bonuses stack.
He could also make an Attack action as part of a Readied Action, so long as he ends his turn within reach of where he wishes to make the attack. Readied Actions are standard actions. He cannot ready a charge attempt. This is because when he could ready the charge, he could take more actions than just a standard action, preventing a standard action charge as part of the charge rules.
If you are able to take only a standard action on your turn, you can still charge, but you are only allowed to move up to your speed (instead of up to double your speed) and you cannot draw a weapon unless you possess the Quick Draw feat. You can’t use this option unless you are restricted to taking only a standard action on your turn.
None of these actions prevent Opportune Parry and Riposte against attacks directed against him.