I guess there is a decent type synergy between Ninjask and Toad (Fire, Electric, and Rock attacks aimed at Ninjask are resisted by Toad, and Grass attacks aimed at Toad are taken by Ninjask), but true synergy needs to extend deeper than that.
For example, Ninjask's main job is to use Baton Pass to get boosts to a sweeper of your choice. You're going to need to think about what things might stop Baton Pass-- Whirlwind, Taunt, Unaware Quagsire -- and then address those problems with your other Pokemon. Cradily for example has Suction Cups, so it cannot be Whirlwinded / Roared away, and it also doesn't really care about anything Quagsire does so long as it's packing a Grass move.
To be honest man, that's just an example of team synergy, but it's not going to work well if the Pokemon themselves aren't solid. Unfortunately the three Pokemon you listed just aren't that good. : (