You have 2 cores on your cpu. No hyperthreading.
So you have 1 assigned to one vm and 2 assigned to the other.
What this means is one virtual machine will use only one core whilst the other can use both.
When both machines are running they will share one of the cores, whilst the virtual machine with the two cores will share one core with the other vm and have one to itself.
Unraid will always have access to your cores so you dont have to worry about that.
Think about it like running programmes on a computer. each vm is a programme and unraid is the os.
I hope this makes sense.