Therapy for child to lie?

I need an outside opinion. My step son, whom I love dearly is going through stuff so his mother put him in counseling/therapy. Now his son hasn’t went through trauma that were aware of. His parents split up when he was a couple months but for the most part are good at co parenting! She even includes me, such a good example for his son. Randomly he started acting out, attitude like most kids have lol but he was doing stuff such as setting the bathroom on fire, lighting toilet paper on fire, saying the dog attacked him when the dog didn’t so the dog would get in trouble, lying about everything. He’s been going to the therapist and playing some type of game, he lies and says he can’t sleep because my so and I fight ect tons of lies about his moms house... they don’t approach this, they let him get away with making serious accusations that could end up with social services involved. They won’t approach it because he gets angry and they don’t want to upset him. If we say enough of the YouTube he has a mental break down, he has to be on it all day! Then he makes up lies because he’s angry he can’t play on the tablet. it got to the point he started screaming and crying while at a relatives becauee my phone was at 6% and I wouldn’t give it to him. I ended up letting him use it because he wouldn’t stop freaking out infront of people. I have to tip toe around him because I’m afraid he will be upset and say stuff that isn’t true, he’s even went to the point of saying we don’t feed him! He got dropped off at 7:30 pm, I had just taken out dinner I made and we were unaware he was even coming but assumed he ate as I only made enough for two people, he said he didn’t eat so I gave him my portion and didn’t eat, because he should have a full belly before I do. Only to find out he lied because my so called his mom asking why he didn’t eat all day, she told him he did and even had desert at dairy queen, but why does he lie about that? And the thing about him going to therapy is the lies are becoming worse and more frequent. It’s not helping him at all, I don’t know why he’s acting this way. He has a very good life, tons of loving family, all the toys he could want. He’s in any extra curricular activity he wants to be in so he’s not bored per say or even lonely. I feel he needs discipline for bad behaviour which he doesn’t have from either parent and when he is lying they don’t sit him down and say he can’t do this crap, he’s 8 years old. Old enough to understand, I think this is spoiled syndrome because he knows he will always fret his way and will say lies to his mom to guilt her into doing things for him like buying toys ect and same with his dad....he knows if he acts out enough that they will bow down and give him whatever he pleases. I want to help him, I just don’t know how anymore.