Having some overlap in and of itself is not a huge deal, but for the reasons that others have stated, it is a good practice to only assign the number of CPU cores that are really necessary, especially if you are constrained in the number of total physical cores available. If you had more cores to work with, or if you were in a cluster that could dynamically reallocate a VM to a host with less contention, it wouldn't be as big of a deal.
I would try to scale back your cPanel to 2 vCPUs and see how it performs. If it performs acceptably, leave it there; as you will enounter less memory overhead with less cores per VM. How to best configure your VM for performance is trial and error, but it is best practice to start off with less and increase as needed.