Yvonne
Since Yvonne is the Main DPS of this team, you'll want to invest into her with things like Skill Levels, Operator Levels, Signature Weapon, etc.
Wedge is also a strong option that you may receive while pulling for Laevatain's Signature Weapon.
Xaihi
You can check out the full guide, but TLDR we want to stack as much Intellect and Ultimate Gain to increase her buffing capabilities. We're currently unsure of the BiS weapon for buffing, but
Chivalric Virtues,
Detonation Unit, or even
Dreams of the Starry Beach are all solid options.
Last Rite
Since Last Rite is mainly here as an enabler, we don't need to invest too much into her personal damage. This is why we recommend
Seeker of Dark Lung. For Gear Set, it doesn't matter too much, but
Tide Surge is good for personal damage and if you ever decide to play Last Rite as the Main DPS, this will be the set you want.
Fluorite
Fluorite is also here to enable inflictions, so
Frontiers is ideal for shortening the long cooldown on her Combo Skill. Potential 5 is a great upgrade for reducing her Combo Skill cooldown as well.
Lastly, you can use Fluorite's Ultimate whenever to apply an extra Infliction the same way her Combo Skill would. This can be the 4th Infliction on a regular rotation. Depending on how much Ultimate Gain you have, this can be every other rotation or more.