Yes you can have multiple lost souls, but you must follow deck building rules. I am assuming this is a type 1 deck so here are the requirements:
Maximum of 1 of each in a deck:
• Multi-colored enhancement, Hero, or Evil Character
• Dominant (lamb icon or grim reaper icon card)
Maximum of 1 of each per 50 cards in a deck:
• Card that has a special ability (text over the picture). Example: A fifty-six (56) card deck may contain only one Authority of Christ, one Repentance, etc. A one-hundred (100) card deck may contain no more than two Authority of Christ, two Repentance cards, etc. A one-hundred fifty (150) card deck may contain no more than three of any individual special ability card.
Maximum of 3 of each in a deck:
• Single-colored Heroes, Evil Characters and enhancements that do not have a special ability.