They're definitely legal, Jagex of course can sue but then again as @Alek said you can literally sue over anything.
For instance, companies like Blizzard will sue as much as they can because they're a multi billion dollar game company so they have the legal team and resources to keep you in court until you can't afford to pay attorney fees and you have to settle.
As far as I know Jagex hasn't sued before and the largest scale takedown was RoW's youtube channel.