Whenever I give a talk on handwriting analysis, I always have someone tell me they and their sister/ mother/ friend write exactly the same way.
What they are talking about is the writing style. People who learn to write in the same environment usually have a similar writing style, unless they have deliberately changed it.
However, that does not mean they the same personality, and it does not mean that, when analyzed, their writing will tell the same personality traits.
Handwriting analysis looks at the placement of the writing on the page, the size, the pressure etc. It also looks at the strokes within the writing. The writing style may be similar, but the placement, size etc. and the strokes may well be very different.
So when you look at writing, thinking of handwriting analysis, be aware that the superficial style is just that – superficial. It in now way alters the ability of the science of graphology to bring out the entire personality of the writer.