How do the Warding Bond and Sanctuary spells interact?

Question

So I (war cleric) and my friend (paladin) want to use warding bond. It says:

[...] While the target is within 60 feet of you, it gains a +1 bonus to AC and saving throws, and it has resistance to all damage. Also, each time it takes damage, you take the same amount of damage. [...]

So the questions are:

1. If I cast sanctuary on myself, does the enemy who attack my friend have to roll a saving throw first before it hits me because of warding bond? Or does warding bond nullify the sanctuary effect on me?
2. Is it okay to cast healing spells inside the sanctuary?
3. If I have the defensive duelist feat, can I use my reaction to nullify the attack I got from warding bond?

Answer 1

Per Sanctuary,

You ward a creature within range against attack. Until the spell ends, any creature who targets the warded creature with an attack or a harmful spell must first make a Wisdom saving throw. On a failed save, the creature must choose a new target or lose the attack or spell. This spell doesn't protect the warded creature from area effects, such as the explosion of a fireball.

If the warded creature makes an attack, casts a spell that affects an enemy, or deals damage to another creature, this spell ends.

1. If you cast Sanctuary on yourself and Warding Bond on another creature, then when the target of Warding Bond takes damage, the rules of Warding Bond would apply. Since you were not the target of the attack, Sanctuary would not take effect.
2. As long as you are not targeting an enemy, you can still cast healing spells and cantrips that don't deal damage.

Per Defensive Duelist,

When you are wielding a finesse weapon with which you are proficient and another creature hits you with a melee attack, you can use your reaction to add your proficiency bonus to your AC for that attack, potentially causing the attack to miss you.

3. Similar to the first question, another creature is not hitting you when you take damage from Warding Bond, so Defensive Duelist would not apply.

Answer 2

Sanctuary only protects the person it is cast on, and only from attacks. If it's only on you, enemies don't need to make the save to attack your ally. The sanctuary isn't nullified, it still works for you, but doesn't affect the paladin.

You can cast any spells or cantrips that aren't attacks while protected by sanctuary without breaking it, including healing, defensive buffs, or even offensive buffs like bless, as long as you're not the one doing any attacking. You can also use abilities that aren't attacks, like a Life Cleric's area-healing ability.

You can't prevent the damage from coming through warding bond with an ability that prevents attacks, because there's no attack. You just take the damage. (What's happening is that you're taking half the damage for the warded ally, but it's represented by them taking half damage and then you taking the same amount.)