Now this has to do a lot with my parents past.

I (17m) life with my mother, my half brother (another father) and my full sister.

My parents had me when they were in their very early 20s. After my mun was pregnant with me, my dad said he wanted to teach me piano (he was a music teacher at a local school). My mum agreed. As soon as I was born, my dad showed his bad sides, gambling, drinking, smoking a lot. When I turned 5, he taught me to play the piano, well taught would be wrong, as he more or less beat the lessons into me. My mum didn't know about it as I didnt say anything. during the span of one year, he became more and more violent, hitting my mum and even attacking her with a knife once whilst drunk. My mum decided to leave him in a rush, for the sake of our safety. Now I don't know if this has to do anything with it, but I was a rough child. my mum had to give up a job, as she had to constantly go to the kindergarden or school, whenever I misbehaved (fighting and doing dumb shit). I got diagnosed with ADHD and my mum decided to resort to medicine (I don't blame her). It worked out and I behaved well. Fast forward a bit and I'm 14. We're on a vacation to see my dads parents who I haven't seen in 12 years (so never really). My dad was also there at that time with his new daughter, about 5 years old. I really liked her as she's been the kind of little sister I've always wanted. My little sister was never on good terms with me, dunno why tbh. 
Fast forward 2 days and we're still there. A stupid family arguement breaks out with two sides. The agressive A-Holes including my father and his bitch sister who claimed that my cousin punched her son (she didn't) and the ones that wanted to talk, including all of my family, my cousin, my grandparents and some other cousins. My dad goes to attack one of the male cousins with a pipe which he blocks. fight ends as soon as my dads older brother arrives. He tells us to leave for our own safety (in a kind way, gave us money for a hotel) and apologised for his siblings behaviour. This incident was the last time I saw my dad. 

I also need to add, that I am still playing piano and if it wasnt for me learning the piano, I wouldn't have got to known the most amazing person I've ever met, who made my life so much more joyable. I know that she would've wanted me to meet up with my dad as well. I'm grateful to my dad that he gave me this gift.

Now here comes the thing:
My mother has been badmouthing my dad forever, and tbh most of those things I would say sound like things he'd do. But I don't hold grudges against people, as life is simply to short for that. My mother on the other hand still hates him and I understand. 
He contacted me and my sister in November 2018, if we wanted to meet up every two weeks again. My sister instantly said no. I don't blame her, She barely got to know this man, only a few times and he just jelled and had a pipe in his hand. I on the other hand agreed. Now I do have the right to see my dad and my mother or anyone else can't do anything against it. She got pissed at me for saying yes, calling me a "betrayer" (haven't heard that for the first time) and saying "do you know what I had to go through, do you know how much therapy I needed to get past his abuse?"
Well I said no but I still wanted to see him. 
We somehow ended the arguement and left it open. My dad contacted me last week, saying he wanted to meet me. How'd he get my number? I didn't care. All I cared about was if he's the real guy. So I asked a couple of questions which he got right. He told me his wife got a second child after the first one and they want to meet their big brother. Now, he did contact my sister but she instantly blocked him. I didn't tell my mum. Instead I told we'd meet at a café and I'd bring along a friend. Time comes and we're at the meeting and talking about how things are. He invites us to his place and we meet the girls. They are lovely and I love both of them. The wife is also very kind and caring. I left with a positive attitude.
I went home and told my mum that "oh yeah, today I met up with dad"
she just asked " what do you mean" so I told hee the same thing I just told you guys. Shw gets furious, screaming at me that she told me not to do it and even if, I needed her permission. 
The incident spread throughout the family in an hour and I got threats from different family members. One said he'd take away my laptop, console and piano (all things I paid for with my part time job money) to which I replied he can go ahead, as I wont back down about meeting him regularily. He took the laptop and the console. well I wanted to go to the police about it but my mum said she'd not file a complaint (I needed parental confirmation or some shit like wtf) 
The piano stayed as my mum convinced her brother/my uncle to stop it).
I'm in this situation where I don't know what to do. 
I understand my mothers worried actions, but she needs to understand how I feel too (which is always last priority in this family).

AITA, does ESH or is NTA?