In the Static Mesh Asset window make sure they have the collision volume around them.
Then to the right, make sure collision is enabled.
Then, if you are spawning them from a class blueprint, make sure it is all setup with collision.
Then, make sure whatever blueprint is doing the spawning has the correct collision settings. (AddInstancedStaticMeshComponents has collision checkboxes for instance).
If all of that seems in order you might play around with the collision presets in those various locations as some options might work better than others.