accident happened just before 10 am on sunday in durham , north carolina .
derek lowe , 38 , and tina lowe , 33 , were pronounced dead at the scene .
northbound train struck pair on property owned by norfolk-southern .
train no. 80 , the carolinian , was headed from charlotte to new york city .
trip continued after about three-hour delay and no passengers were hurt .
man who met pair while collecting scrap metal said they were homeless .