Mari would go for a minigun/machine gun. She enjoys a bit of wildfire but dislikes having to reload the gun. However, she might be afraid of the sound and might choose a bat or hot knife instead.
Kel would go for guns too, any would work. I figured a revolver, rifle or sniper might work but for melee they'd choose a katana.
Elias would go for... an elephant. Now hear me out elephants have been used for years for combat, that they can double as a pet and weapon. Besides, it not like Elias can do much- not compared to an elephant that can stomp you to death.