Hey!
Try this. Once your objective 1 is complete, you could put in the 'On Activation' field of either a trigger or waypoint: obj1. For objective 2, in the 'On Activation' field: obj2 etc... In a final trigger, place in the 'Condition' field: obj1=true AND obj2=true. This is followed by making the trigger execute the desired 'On Activation' field commands.
Basically, when a objective is acheived it makes obj1 true. The same is true for obj2. In the final trigger, obj1 and obj2 must both be true AT THE SAME TIME, then the 'On Activation' field will offer it's actions.
I don't think I explained this well and I might have got the "obj1" and "obj1=true" mixed up. But, the concept it right. Good luck!
Scooter24