Sunflora, Ludicolo, Cherrim, Exeggutor. Cherrim has both Aromatherapy and Heal Pulse (And 6 SpA with Everstone, which helps). Most of the team will be self-healing w/synthesis as well. Ludicolo will take and maintain threat throughout.
Things we'll need:
Everyone who gets Dispel or Shadow Mend should pick it up.
Strata could do with HP Ground 6, Earth Power, Giga Drain, Energy Ball, Rain Dance, and Rock Slide.
Roserade will want HP Water/HP Ground, Water Sport, Mimic (!), SolarBeam, Grass Knot, and Giga Drain.
Castform will want Weather Ball, Hydro Pump, and Ice Beam.
Necturna would like HP Ground, Horn Leech, Gravity, Power Whip, Giga Drain, SolarBeam, Grass Knot, Stone Edge, and I THINK that's everything.
I've listed all the moves I think we'll need, but if I've missed any I'll tell ya.