First Team, any suggestions?

So first team, I built it using just intuition and also Gengar is a MUST HAVE! Will not do a team without him. Anyways, I built a classic sweeper team so let me know what I can do to fix it! Also want to keep the Latias if I can.

Sp. Sweeper
Gengar F @(can't decide, is his mega item still banned?)
Cursed Body - Modest
Shadow Ball
Dazzling Gleam
Sludge Bomb
Haze

Sp. Sweeper
Wishiwashi F @Shell Bell
Schooling - Modest
Aqua Ring
Scald
Ice Beam
Earthquake

Atk. Sweeper
Charizard F @Charizardite X
Tough Claws - Adamant
Belly Drum
Earthquake
Fire Punch
Protect

Atk. Sweeper
Bewear F @Groundium Z
Fluffy - Adamant
Thunder Punch
Ice Punch
Hammer Arm
Double-Edge

Tank/ Staller
Shuckle F @Leftovers
Sturdy - Impish
Toxic
Protect
Sandstorm
Stone Edge

Support
Latias F (duh) @Latiasite
Levitate - Timid
Ally Switch
Heal Pulse
Dragon Pulse
Tailwind

The idea behind this team is to use Latias as a starter 99% of the time, the timid nature gives the ability to likely go first and get tailwind out. My other starter just depends but 80% of the time it will be Charizard. This way my first 3 turns could look simple yet effective. Tailwind and Protect, Ally Switch and Belly Drum, Heal Pulse onto Zard then either fire punch or earthquake, and Latias has levitate so it isn't affected. The other 2 pokemon I choose are just counters at that point. Likely Shuckle and then either Gengar or Wishiwashi.

Hi. I don't know what format you are playing (Smogon or VGC), but this is a Competitive Pokemon forum, so the team has to be competitive. There are some things that you haven't had a knowledge about:
1) Checks and Counters
An ideal team is a team that has no weakness (every Pokemon's weakness should be able to be checked, at least, by the team's other Pokemon). With an instant glance, I know that Mixed Greninja will wreck this team. You can say that Bewear resists Dark and Latias/Wishiwashi resist Water, but they are slow and not bulky that they can be brute forced by non-super-effective moves by Greninja. Offensive Garchomp can also destroy this team after Latias faints. Pretty much all Fairy Pokemon are your weakness. Gengar is strong offensively, but defensively, it's so frail. You can't use it to tank much damage.

2) Item Effectiveness
Every item should be able to be used at any time. In your team's case, you have 2 Mega Stones on your team. I know that you can pick between 2 Pokemon to suit the battle, but it's not worth having a Pokemon item-less (your team can only turn Mega once per battle). Also, why do you give Groundium Z to Bewear, when it has NO Ground moves? Just, why?

3) Pokemon Role
Shuckle is NOT meant to take damage. It's true that it has insane Defense and Sp. Defense, but its Health is also insanely terrible. Gengar is a sweeper, that's right. A sweeper should have a high Speed, high offense stat (either before or after setup), and a wide movepool so that it can not be easily forced to switch. A sweeper should NOT have status moves other than self-boosting moves. Why does your Gengar have Haze?

That's what I can think for now. My advice for now is, you need to rebuild the team using what I typed, at least.