Lanefan
Victoria Rules
And that's also absolutely horrible; and just more 3e-think.That's not really that hard. Actions don't happen simultaneously, so assuming the target failed both saves, he would be subject to movement by both casters on their respective turns, per the spell's text on what the caster can do to the target.
Yes the actions (of any kind, not just this) are only dealt with on a player's "turn" but they're assumed to be ongoing in the fiction throughout the whole round, otherwise what you end up with when you try to visualize it is ridiculous.