The best way to do this is through HDL. This flow is explained in UG908 on page 137/138. You would take the trigout of ILA 1, and pipe it to both of the other ILAs trigin ports. Then take their trig_in_ack and and/or them together depending on the trigger situation. You might need to play with the timing a bit, but there is a timing diagram for reference on page 139.