Need advice on 8 year old stepson

My 8 year old stepson is acting out in an extreme fashion. He's an only child.

He has stolen credit cards to to buy games on his Xbox 3 different times. The first time his dad's card was already on file for billing purposes (he removed it after the incident), the other 2 times he got his mom's card out of her purse and used it.
He also has bathroom issues. He'll be 9 in 3 months. Up until about 6 months ago, he was still pooping or peeing his pants once every week or 2 at school. He acts like it upsets him when the other kids make fun of him, but he wouldn't stop doing it. He still won't wipe himself out of laziness. Just a few weeks ago, his mother fussed at him because he didn't wipe himself and he left some poop on the back of the toilet. She made him clean it off. So the next time he had to poop, he took his Halloween bucket and pooped in that in his room rather than go use the toilet. What the world??

His mother spends more time texting on her phone with guys from dating sites than she does paying attention to her son. He failed the second grade. He yells at her and is very disrespectful toward her, but like I said, she won't pay any attention to him. She'll tell him she's going to take him to a movie or something and then she'll back out. He doesn't act this way with his father (thank goodness, I couldn't stand to be around that...). He is still sneaky and lies sometimes when he's here. He'll hide soiled underwear from us even though his dad has told him it's ok, we won't be mad at him. But overall, he doesn't act out nearly as bad when he's here as he does when he's with his mother.

My husband doesn't seem to realize how bad his behavior is to anyone on the outside. I think his behavior is atrocious and he needs to be seen by a psychiatrist immediately.

Any insight would be appreciated.

Kids are kids. Bathroom issues can crop up with any kid at any age when they are dealing with stress and anxiety. Getting angry or blaming him is counter-effective, you're right. This isn't about him misbehaving. This is a sign that there is something else that is wrong. You actually answered your own question on that issue when you mentioned how his mom spend much of her time. I can relate with your son on that. This boy is plagued with confusion, frustration and emotional neglect from his mom and he is acting out to get any type of attention from her. He's not bad. His mom is causing this and you need to speak to your husband about gathering evidence and seek custody or more time with him. There could be other things going on while he's at his moms. I don't like to say this often, but there should be an investigation. Have you talked to his school. Has your husband?
Again, I know this is a stressful situation. But just realize that his behaviour is not in his control. He is too young to know how to manage his emotions and rationalize everything because he has to deal with adult situations in that his mom is more focused on finding random men than him. That is heartbreaking.
I had to deal with it when I was living with my mom and I always thought, to this day I think, she would have been happier without me. But that is minor compared to how my step-mom treated me. And when I was over at my dads that's when I would soil myself at night. It only happened at my dad's and my step-mom would humiliate me because of it. She was intimidating and treated me unfairly. My dad spent some time with me, but because of his shift work he was often working or sleeping. I now have an awkward, broken relationship with that whole side of my family.
Just giving you some perspectives on what your step-son may be going through. He's not crazy or needs to be hospitalized. He should see a counsellor first and a pediatrician and then they can assess what needs to be done. But I really think that because it's worse when he's with his mom that that's where the problem lays.

Is the bathroom issue one that is medical? Then you might be dealing w/encopresis. I'm EXTREMELY familiar w/the subject. I'd get a medical opinion on it.
But you said he pooped in his bucket. Sounds like there was Intent so there might be a Defiant Disorder there which I also have experience with. Kids this age have very little control which is what they want. So they use their bowels as an answer. That they can control.

Yes I think he's definitely looking for attention. And if it's thru bad behavior he thinks "at least I'm getting attention."

I would seek professional help in this area. I wish you all the best.

He needs to be seen by a therapist who has experience working with kids. You can contact his pediatrician who can refer you to someone who takes his insurance. His environment is going to have to change to see changes in him. If his mom continues her behaviors, he will continue his.