Goldorak's got you on the right road.
You'll want to next Dynamic Groups (DG's) inside a master DG. So you'll have a master DG that has 3 objects in it, and you'll select a maximum of 1 of those 3 objects to spawn. Then you have 3 DGs inside the master, each with their own objects inside them and at the PI's you've indicated. The master spawns one of those three groups, and when that group spawns it will spawn whatever is inside it.
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