In my style of aikido, tests from 4th kyu onward finish with randori. 4th kyu requires randori with one uke, 3rd kyu with two uke, 2nd kyu with three, 1st kyu with four, and shodan and up with five.
When there are three or more uke, the attack is usually ryokata dori and the technique is usually kokyu nage. The uke attack simultaneously (no waiting); the idea is to avoid being caught for as long as possible, where being caught means being grabbed by two or more uke at once.
I've posted a game that simulates this style of randori. You may be able to play it if your browser has a recent version of Java. You can find the game here:
http://home.rochester.rr.com/draz/Randori
-Alvin