The idea of a MAC address is that they are intended to be globally unique identifications. I am not sure how you are seeing the same MAC address across multiple devices, this should never happen. I know it perhaps does not answer your question but it should never happen in the first place.
None the less, you can try MAC address spoofing, and a quick Google search reveals the following link: http://www.robmcghee.com/android/changing-the-mac-address-on-android/
