Zada, Hedron Grinder

If you cast an instant or sorcery spell that has multiple targets, but it's targeting only Zada with all of them, Zada's ability will trigger. The copies will similarly each be targeting only one of your other creatures. You can't change any of the copy's targets to other creatures.

The controller of a copy can't choose to pay any alternative or additional costs for the copy. However, effects based on any alternative or additional costs that were paid for the original spell are copied as though those same costs were paid for the copy.

If the spell that's copied has an X whose value was determined as it was cast (like Rolling Thunder does), the copies have the same value of X.

You control all the copies. You choose the order the copies are put onto the stack. The original spell will be on the stack beneath those copies and will resolve last.