That's all that I have for now, What pokemon would you recommend I add?
I'll be that guy.
On Charizard, forsake Aerial Ace. It's a terrible move. Go for Focus Blast, it allows you to defeat Tyranitar and Heatran, who otherwise stop Megazard Y. Protect is terrible unless you're in doubles. You can go for Roost (for survivability) or Dragon Pulse (to hit Dragons), instead.
Curse Umbreon is usually easy to set-up on. Curse-boosted Payback won't do much to anything that resists it. In fact, Conkeldurr, Bisharp, Lucario and Megawile can use laugh at this guy. If your Umbreon is hit by an opposing Toxic it becomes useless, too. I would vouch for a classic Cleric set, but that's up to you.
On Trevenant, my only complaint is the "4 Sp.A". Since Horn Leech is physical, you can put 4 Atk instead.
As for other team members, you need resistances to Dragon, Flying, Ice and Rock to cover your team's weakness. A Steel-type can cover these, but Aegislash and Jirachi aren't good choices because it stacks Ghost- and Dark- weaknesses with Trevenant. Since you lack a physical wall, Skarmory can help in this spot, it covers Flying and Dragon, can switch on Toxics, and even set up SR for you... But even then, it stacks some weaknesses you already have. Bisharp is another option, since you lack a physical attacker, it covers all those 4 types I listed, and you can cover it's weakness easily.
Considering the sun provided by Megazard Y, you could have Pokemon that benefit from it, such as Heatran, Volcarona and Venusaur. Dragons who use Fire-type moves like Fire Punch Dragonite, Fire Blast Garchomp and Goodra can use the sun boost to get opposing Steel-types. The fact they resist Fire, and can take Water attacks are bonus.
Lastly, you'll really want a Spinner or Defogger to remove Stealth Rock from your field. As for which of them, build your team first, then decide the spinner/defogger.
If you're reading this, CONGRATULATIONS!! You're wasting your time!!
For Mega Charizard Y if you really want Flying STAB move, go with Air Slash over Aerial Ace since your Spatk is going to be higher. If you didn't breed Dragon Pulse on then go with Focus Blast (Coverage) or Roost (Healing) over Protect.