[VGC] Need help building team for June International (Yveltal maybe?)

I'm planning to play in the June International, which means I need to throw a team together quickly. I haven't been playing in the VGC, mainly sticking to BSS, so the meta is fairly unfamiliar to me. I've started doing a little research on my own, but don't feel confidant that I'd put together the greatest team I could without some advice.

I have an Adamant Kangaskhan that I'm very happy with, and would like to be one of the pillars of the team. Generally in BSS, I run her 252HP/252ATK so that I can survive opposing Mega Kangaskhan Low kicks while possibly OHKOing back with my own. However, I'm thinking that Kangaskhan won't be the only hard hitter I have to worry about, so would 252ATK/252SPEED be more recommended? I'm thinking the following moveset:

Double-edge
Fake out
sucker punch
Earthquake

Normally I use Low kick rather than Earthquake for the last slot, but I'm thinking Earthquake is going to be better here. Let me know if my thinking is wrong.

I'm thinking pair this with Yveltal. Unfortunately for me, I don't have a Jolly Yveltal. I have Modest, Timid, and Calm. I'm really torn on which nature to run. I'm leaning towards Modest because its my understanding Modest Life Orb will OHKO several important threats that the others won't, but maybe Timid to speed tie with other Yveltal, or even go defensive. Calm could be cool for Tailwind/Taunt/Oblivion Wing/(dark move). Otherwise, with Modest or Timid, I'm thinking

Oblivion Wing
Dark Pulse
Sucker Punch
Foul Play

I guess one of the cool things about these natures is I take less damage from opposing Foul Plays, but I probably would rather have the strongest Sucker Punches. I have what I have, though, I don't think I'm going to get a better one before the event starts.

To pair with those, I'm thinking Liepard. Fake out/Taunt/Foul Play/(Thunder Wave or Swagger). Is Timid the preferred nature? I'm thinking with a Focus Sash.

I also have a Klefki I think would work with these three. Just the standard Swagger/Thunder Wave/Foul Play set is what I'm thinking. Unsure on the last move, maybe protect? How do I run the EVs and nature? Leftovers is the preferred item?

I get one more Legendary. I think Kyogre is what typically goes with these Pokemon? I don't have a Kyogre, but maybe could trade for one quickly enough. Is there a different Pokemon I could use though? I have a Quiet and a Bold Rayquazza, would either of those work? I have a few Zygardes and Xerneases, as well.

For the last slot, I was thinking Ferrothorn to fight against Xerneas. Brave with Gyro Ball/Power Whip/Explosion/Leech Seed. Or possibly Sassy with mixed defenses? I would also like Thunder Wave on it. Replace Leech Seed or Explosion (maybe keep Explosion for Brave and Leech Seed for Sassy)?

I'm not really tied to any of these Pokemon, except Kangaskhan. So I'm totally open to suggestions. I've also considered a Calm Togekiss to go along with Yveltal for dual Tailwinds, as well as further Thunder Wave spreading. I could try Gengar for STAB Sludge Bombs, though the amount of sucker punch running around makes me hesitant of that. Aegislash is also a consideration.

Let me know some suggestions for items, EV spreads, or whatever else.