Am I the problem?

Hello, it was my birthday yesterday and like almost every year since my stepfather came, my birthday is always crap. We get insulted a lot or accused of doing something we shouldn't and we've even been threatened etc. My brothers had these problems too when they lived there together but suddenly since they moved out they've repressed everything and say that it was never like that and say that they are the problem. They don't notice anything from home and say that what my mother says, for example, is true as a matter of principle even though my sister was there and can testify that they are lying. They lie a lot to other people and drag people into it who have nothing to do with it and the worst thing about it is that they contradict themselves because one day she says what my stepfather told us isn't true and when, for example, a week later my grandmother is here she says what my stepfather says about us is true and that we are supposedly always so ungrateful and just cause trouble etc. And we are treated like dirt by subconsciously I have the feeling, superficially he acts like he does a lot of things for us but then talks shit about us or lies and for example actions happen like he puts us on the guest wifi and I found out the password with a QR code scanner and it's called 'for you ungrateful people' and my mum always says that what he says is just a joke or when he threatened to hit us etc. she says he doesn't mean it, he won't do it or even supports it… I've been accused for years of supposedly only having something against him and that's why I don't like him but that's nonsense if I don't like something then I say so and it worked with the partners before him and I had nothing against the people or I haven't told my mum about the password for months so as not to cause unnecessary stress, to give him a chance for things to get better but they haven't. The text is probably quite confusing but I'm doubting and wondering if my perception is simply wrong or if it's normal to have such problems. I don't know and my therapist has already tried to talk to my mother and she said that she will improve her attitude but nothing happens