Thank you for reaching out to the hotline. Being a good parent is one of the toughest jobs for anyone, but parenting a child who probably had so many different guidelines set out for him from the various households he has lived in makes it even more difficult. You are wise to want to get a handle on his behavior now.
Therapy, positive and negative reinforcements, and time outs are all very appropriate ideas for the type of behavior your stepson is displaying. If both Mom and Dad are on the same page, that helps. In addition, as you struggle to find something that works to improve his behavior, keeping a calm demeanor even when you want to shout is a must in front of him.
If your son has never had an assessment in the past, consider having one done by a clinical psychologist. The thought of having your child diagnosed with something is certainly a scary thought, but often, once something is diagnosed, you can get a better idea of how to handle the situation or what direction to go in.
If the therapy you tried was behavioral therapy, then consider working with a child behavioral therapist again. Ask your pediatrician or friends in the medical field for personal recommendations. Most times, they will meet with the child alone, the parents alone, and then the child and the parents as a group. A specific plan can be developed as to how react to a specific behavior. A good therapist would probably even enlist the opinion of your son. If he is able to help set up a plan, then he might take more ownership in it.
In the meantime, to avoid his late-night trips to the kitchen, think about somehow safely blocking off the kitchen or investing in a security system with motion detectors so you can intervene immediately. This next suggestion will call for absolute consistency and might interrupt plans, but if he steals when away from home, take him home immediately. Have a talk with him about how stealing will be handled so specific expectations are established. At first, intentionally make some trips that you really do not have to make, and when he steals, take him home right away.
If these same misbehaviors are an issue at school, then set up plan with the principal and next year’s teacher before the school year begins. The more consistent you are, the better. If you care to discuss this in more detail, consider giving the hotline a call.