Jolly is the preferred nature on Mega-Kangaskhan so it outspeeds more stuff. Parental Bond and a +2 boost from Power-Up Punch give you more than enough power. Earthquake is also better than Aerial Ace. A STAB max power Return is stronger than a super-effective Aerial Ace:
Return: 102x1.5=153
Aerial Ace: 60x2=120
Earthquake allows Kanga to destroy Steels that would other wise tank its moves. Ground gets nice coverage anyway. Gliscor can handle the Fighting types Kanga can't (and Gliscor isn't gonna spam Earthquake anyway; its role is a more defensive one).
As for your 3rd Pokemon, a specially defensive water type is probably a good idea. Gliscor is your physical wall, so that side of things is already covered, Gliscor also very much appreciates an Ice and Water resistant poke, and your team could use something that dishes out special attacks so you aren't walled by opposing physical walls.
Rotom-W fills that role nicely:
-Rotom Wash w/Leftovers
Nature: Modest
Ability: Levitate
EVs: 232 HP, 56 Sp.Attack, 220 Speed
Moves: Hydro Pump, Volt Switch/Thunderbolt, Will-o-Wisp, something
-Rotom Wash w/Leftovers
Nature: Calm
Ability: Levitate
EVs: 248 HP, 28 Sp.Attack, 232 Sp.Defense
Moves: Hydro Pump, Volt Switch/Thunderbolt, Will-o-Wisp/Thunder Wave, Pain Split
Vaporeon also makes for a beautiful bulky water type:
-Vaporeon w/Lum Berry or Leftovers
Nature: Bold
Ability: Water Absorb
EVs: 252 HP, 248 Defense, 8 Sp.Defense
Moves: Scald, Wish, Protect, Ice Beam/Roar/Toxic
If you need a Razor Fang, try the
Items Quick Trade Thread.
Oh, and I wouldn't recommend using this team for Doubles; singles and doubles are quick different battle environments, and what works in one rarely works in the other.