Re: Telekinesis - Earth Only
I'd say any characters wanting to ride the gravel-bus would have to make that decision on their own & make DEX checks / grabs / etc. in order to stay on top. If PCs didn't want to be affected by the gravel, they can avoid it with minimal effort. The player controlling the gravel would not be in control.
Same for TK - Earth only. If that player lifts a large section of earth with people on it, the people can get off easily if they so desire. If they want to stay on, it will be difficult for them (DEX rolls, grabs, etc., GM deciding how bumpy the ride is).
If the player has TK - requires Earth, then the ride can be easier (DEX checks etc. not required), and the TK player can attempt to carry others against their will (bowl or spherical shapes, shifting ground, earthen hands grab ankles, etc.).