If your datastore has certain amount of IO's it can serve, the VM's can use them without any limit. If all the VM's have same amount of shares all of them will have access the storage and use the IOPs they want to.
If you want to limit IOPs usage at datastore level, you can always enable Storage IO control which will make sure the IOPs are spread across the VM's on a particular datastore.
See this for more info
VMware vSphere Storage I/O Control for Shared Storage | United States