MILWAUKEE (AP) – Milwaukee police are investigating four apparently unrelated deaths and a series of five nonfatal shootings that happened in a nine-hour span overnight.   In the first case, a juvenile suspect is in custody for allegedly stabbing and killing a 25-year-old relative Wednesday evening.  Then, just before midnight, a shooting in a barbershop left an 18-year-old man dead and a 21-year-old man with non-life-threatening injuries. A 26-year-old man is in custody.        About an hour later, a 34-year-old man was shot dead inside a home. No suspects are in custody in that case.  Soon afterward two men in their 20s were shot and injured in a street. In separate shootings, a 52-year-old man and 17-year-old boy also suffered non-life-threatening injuries.  Police are also investigating the death of a 3-month-old infant.