Supervisor getting another PhD student with the same project?
Having a close colleague with whom to discuss tough sticking points, potential research ideas, etc. will be INVALUABLE for you. 

There is nothing quite so lonely as being one of the experts of the world on a very narrow subject and never having the opportunity to discuss that subject with another person who shares your understanding. 

You will likely produce better work as a result of having this other student around. And you two can collaborate.  Don't think of this as zero sum. Think instead about collaborative potential and about this student as a sounding board. Some of the greatest research I can think of was produced by pairs or groups.