Each person inherits different segments from their parents. Thus each person's DNA is different and the overlapping segments of different family members are extremely useful for the DNA Matching results and your genealogical research in general.
We recommend first testing the oldest members of your family to go as far in your research as possible and not to lose precious time in gaining unique data. We will take care of storing it and helping you use it in order to make new discoveries about your family history.
If you're interested and want to purchase a DNA kit, please visit www.myheritage.com/dna.