The owner of that building is public record. Looked it up for you.
This is for the 1120 Pacific Beach Drive:
Cunningham San Diego LLC
P.O. Box 3634
Rancho Santa Fe, CA 92067
There appear to be 6 units in the Haines Street address. Without the unit number, can't help you there.
Not sure I understand what you are trying to figure out, but if a tenant is lying on their application it's not a good sign. Don't rent to them! Not totally sure why you need to reach their prior landlords but that's your business.