Once there is a consistent consequence he may start to get the message. Just stay on it. It sounds like he is a strong willed kid, so he will try and chip away at you until you give up. Just stick to it, consistency is the key.
We both punish him she carries out the punishment that I give him. I have told him and talked to him about how wrong stealing and lieing is wrong and the consequences. I have not yet got to be consistant with punishment since this is a new thing for me but I will consider what you say and I will try it and see if it works. We are just both at our wits end. He shows no remorse as to what he is doing
Does he know the implications of stealing and what the consequences are and why it is wrong? If not, then explain it to him, if he does then consistent punishment is needed.
What is his consequence for stealing? If it is writing sentences or chores around the house then he needs that done everytime he steals. Also is the aunt disciplining him during the week or just waiting till you can discipline on the weekends? If she is waiting till the weekends, then that may be way to long after the fact to punish the child. '
Education on why stealing is wrong and consistent consequences is vital. Im not saying yell or hit or degrade the child, but the child needs to know that everytime they steal, the same consequence will be given, no less and no more.
Most parents wont agree with what I am saying, however this is exactly what my stepson's therapist told us last night considering some of the same issues. You may get tired and may feel that it isnt working, but just keep on it and always stay consistent.