I'm extremly worried for my siblings

I'm well aware this is tmi, but I'm the eldest sibling and the way things are looking for my younger ones, I doubt they can even make it out into society, honestly I doubt even I can, but I don't ain't that for them

My first younger sibling has severe autism, and as of this year, they keeps throwing 'tantrums' for when you tell them not to do something wrong, give them advise, or when things don't go their way, they express this by throwing things around, crying (really loudly, and by making exaggerated noises while their at it, sometimes there's tears sometimes there's none) and they may even hit and push the people around them. They get angry really easily now infact, and will also stick out their tongue and literally act angry (crossing their arms together and such) It's can all be very theatrical, and I'm partially convinced it's always mixture of their school environment and what they watch online (kids content such as the your grounded for xxxx years guy, to a boca vids, etc, and I even hear the same exagerrated crying from the videos) Why this is extra worrying is because they never really reacted this way before, and their around my age, we aren't that far apart. I want to know what I can do, as my parents are quite lax, besides my mother, but she's quite busy about this, even though I've told them about this worry before and why i think that is, and they are actively seeing it. Honestly my parents are quite forgetful when it comes to their kids I realise,but like I said with my mother, they are both extremly busy people.

I brought up this sibling first, as I think how I react to them is absuletely not the best either, I get way to heated and angered easily, now I just resolve with shutting myself in my room before I say or do anything awful. Though the worst thing is when they push around the youngest sibling during their mood switches, at times I slapped them because of how inraged I get. I feel mostly responsible as my reactions are horrid, and ever since we were younger we fought with eachother quite frequently, only now it's died down after a big incident when we fought, but I feel like they picked up some things from me, such as how I used to stick out my tongue and point when I figured out it annoyed them, yes I was quite the wretched brat, but the point is they do that now, plus I'm still learning to regulate my own emotions (no I don't do that anymore)

I also wish they would hit themselves less when they felt overwhelmed, but it has died down since the past.

My youngest sibling, who is only diagnosed with severe adhd is already been in year 3-4 in primary school, they can't answer questions such as their favourite colour or what they did in school, they don't really get social cues, and randomly touch strangers, can be quite loud or too quiet. I'm extra worried, as since we aren't fully related, they spend part of their time by their own mother so I'm not sure how she's teaching them, but ik my father isn't helping with shit, especially with how petty he acts to his ex gf, his ex wife (my mother) even if it's the matter of his children. He only cares if something embarasses him or if it wounds his pride, that's it. My youngest sibling also repeats specific things such as 67, or other one time phrases repeatedly, as it gives a reaction, but they say really nothing else, nothing personal, no full sentences, that's what worried me the most. I'd liked to believe their mother's got this, but maybe it's because of my own family I doubt.

I probably have a lot of things wrong with me myself, I lost the therapist I had as I didn't share fast enough, and my parents thought I had to share everything wrong with me immediately, and well I never got one back, my mother told me I can tell if I need one, I probably need to get that back, but it seems troublesome, I wont trust easily once more, it'll take time, I'll waste time, and money, it isn't worth it (tmi) but I'm diagnosed with adhd as well. I dont want my siblings to end up as miserable as sad as me, even though everyone around me is convinced im the only one who can live a 'normal life'


None of this is explained properly, I typed everything out in one sitting