Would the tempest cleric's Destructive Wrath max out both damage rolls fir lightning spell or just one? Because lightning arrow has both the to hit damage (4d8) and the AOE damage (2d8), so could i maximize both rolls or just one? Also I keep hearing mixed things about whether the target takes to AOE damage or not. Some people say no, some people say yes if the arrow missed, and some say yes because the target included in the AOE sphere. Thanks for the help!

Tempest Ability: "When you roll lightning or thunder damage, you can use your Channel Divinity to deal maximum damage, instead of rolling."

Lightning Arrow: "The next time you make a ranged weapon attack during the spell’s duration, the weapon’s ammunition, or the weapon itself if it’s a thrown weapon, transforms into a bolt of lightning. Make the attack roll as normal. The target takes 4d8 lightning damage on a hit, or half as much damage on a miss, instead of the weapon’s normal damage.
Whether you hit or miss, each creature within 10 feet of the target must make a Dexterity saving throw. Each of these creatures takes 2d8 lightning damage on a failed save, or half as much damage on a successful one."

The target damage 4d8 and the aoe 2d8 are two separate damage rolls. You can only maximize one of them with your Channel Divinity.

The target is within 10 feet of themselves, so yes, they would also need to make the dex save.

Great, thank you so much!