Since your new at this you may want to get a lady with as many reviews as possible. Trust me you will have a better experience.

To answer your original question, no they are not independent, the reason the phone number is the same is that they are actually an agency.

That said, they are a very reputable agency, and I would not have any reservations in using them again.

Remember the first reviewer sets the profile.
So while some agencies, will try to conceal the fact the girl works for an agency, this agency has a decent reputation. As you may have done, always google the phone #. It's an easy jumping off point to start your research.
Sometimes a young escort will share a cell phone with a gf. The newbie young escorts evidently dont see the red flags shared cell phones raise.
Bottom line, newbies should avoid this situation.

I have not seen any of them but several young providers within my hobby area use a common shared complex for work.  They may also share a phone.  The idea being that if a client calls, there is always someone available.  The fact that they do not work for someone else may make this form of co-op more palitable for some.

An arriving client is ushered through a common area to a private room...  I just don't care to have others outside my door.  Turn off for me.

Personally, I feel several women working from the same location raises the visible profile several notches and makes me uncomfortable.  ONE indiscreet provider can bring LE down on all.  
skb