Mine switches to my daughters info by itself also. My wife, daughter and I are all logged into my iCloud account on each of our iPhones (plus my iMac and MacBook Air) so that the "Find iPhone" app will show the location of each of our devices. "My Info" never switches to my wife's information, just my daughters?????
I'm now trying the "Don't Allow Changes" function under Settings/General/Restrictions/Allow Changes/Accounts - to see if that will keep it from automatically changing.
Will try to report back if this works. I do not know what triggers the automatic change.