Library telephone books will aid you in finding peoples addresses. Alternatively, contact someone who they may have known to see if they know anything about them. Old School and sports club records and pictures can be informative as can Parish Magazines. Non-Conformist periodicals can be found useful in the same way. Seek proof all the time.
Relatives can confuse people and events outside their own time.
If you can jog peoples memories by a photograph or a document than this will be even better. On a first visit you might not find out very much when interviewing a relative so a second visit is best to consolidate information and facts. Remember that some of us cannot remember people on a school photograph twenty years ago. Given time they can sometimes remember quite useful additional facts which will both confirm your research and enhance it. Check newspaper indexes for mentions of the family and Electoral lists for addresses.