Forretress: You could try double edge over swagger.
Skarmory: toxic over steel wing
Marowak: If you want a Hidden Power, try bug. When crystal comes out, put swords dance over sandstorm.
Kingdra: Since it's a STS team, try whirlpool & toxic over 2 of the attack moves.
Magneton: Maybe drop it for Shuckle with wrap, toxic, rest, & sandstorm, otherwise, put sandstorm over T-wave
Gengar: Hrmm, no. T-bolt or psychic, giga drain, confuse ray, and destiny bond is what I use. U can put haze or whatever destiny bond.
Overall: 3x fire weakness. Aside from Skarmory, you have no real way to take advantage of spikes. Crystal NickWak and Gengar should be good enough sweepers if used correctly.
How to ruin a Snorlax: