This is a rather complicated spell so try to describe everything in great detail. At the moment it's still unclear how a lot of this will work and how you will deal with edge cases. Remember that with triggers you can do just about anything, so we can't assume that you mean "like X ability" when the sky is the limit.
Here's what I ASSUME you want:
1) Tornadoes act like the Locust Swarm ability, meaning they're leashed to the casting hero. If not the case, then what does "moves randomly in N range" mean exactly? If they Wander does that imply the use of the Wander ability or just randomly triggered movement? This is very unclear and how random should the movement be if it's triggered?
2) An individual tornado can interact with one enemy unit at a time, during which it'll stun the unit, move it around itself, before doing a knockback effect that sends the unit flying as well dealing damage at the same time. This "spin" effect is NOT the same as the Cyclone ability and the target can be damaged by other units while this is occurring, so it's NOT invulnerable.
3) Tornadoes expire after a few seconds. If so, is this a summoned unit expiration timer? Can you select the tornadoes? What happens if an expired tornado is in the process of spinning a unit? Is it not a duration and instead based on max distance traveled? If yes, how does that work with the wandering movement?
4) A unit can only be affected by one tornado at a time and gains immunity to all of the tornados during and a little bit after this effect. This immunity means it can only go through one spin/push cycle every few seconds and cannot say for example be thrown from one tornado immediately into another tornado, permastunning it.
I'm not planning on creating this myself but if I get bored I may give it a shot. I just wanted to emphasize that a deeper explanation can really help get you exactly what you want as well save the creator's time since they won't have to make any assumptions. Perhaps it's more simple than they imagined.