I have something similar to that in the Content Examples of the plugin where 4200 animated mannequin instances are spawn inside a volume on begin play.
This is done just using 1 Hierarchical Instanced Static Mesh Component, and calling the “Add Instance World Space” function through blueprint.
A simple setup could be to have a bunch of sockets in the Stand model and when calling the Add Instance function you pipe in the transform of a random socket into the instance’s transform.
Cheers.