My friend group is falling apart, please help!!

Hi I (14F) just started year 10 and I feel so horrible about all the drama that happened in my friend group in year 9 as a lot of it has carried onto this year. Sorry this is going to be a bit of a rant.
So I have had a great group of friends since year 7 (The OGs). Then some drama happened at the end of year 8 with one of them (let's call her Lara) and she left the group - that's a whole other story tho so I won't go into that. However, she had brought into the group someone else (let's call her Tiffany). I didn't really talk to Tiffany because I didn't know her...I didn't really have an opinion of her, but she kind of just joined the group. And then in year 9, there was a new girl in our form (let's call her Issy). Someone in the group was made her "buddy" to show her around the school and stuff, so naturally, she began sitting with us at lunch and kind of integrated herself into the group.
Now the drama starts. So, Issy had kind of made herself part of the group, she steers a lot of the conversations towards her (tbh I've never actually heard her talk about someone other than herself unless it's to put someone down). When everyone had accepted her, she was being very passive aggressive towards me for some reason, I didn't like her much, but I was always nice to her and I never let it show. She said stuff to me that were just rude even though she hid it behind a smile. Once she came up to me and she said "let's be honest, DofE is just an excuse for lazy people to get outside" i was very invested in DofE at the time, my expedition was the next week. I am also by no means lazy or unfit - I do training in rock climbing and competitive gymnastics and dance for musicals in the west end. So I decided to myself that I didn't consider her my friend since she clearly didn't want to be. I told my (much closer) friends in the group of what she had said and they said that they agreed with me saying they noticed it too and it was completely unnecessary.
So another friend in the group heard about this "beef" and (bless her) she arranged for Issy and I to talk it out. I was rlly grateful to her and we are still great friends. So anyway during this talk, Issy just kept defending herself saying that she was completely justified in whatever she had said. I was in disbelief, like here I am calmly explaining to her that I was upset (something that I don't usually do - I have depression and severe anxiety) , and she was just basically saying that I was silly and overreacting.
So I kinda just ignored her for the next couple of months. She was still in the friend group and nobody else seemed to have as much of a problem with her, but then again, she was only being rude to me!
So back to Tiffany now. Towards the end of year 9, we had a PGL trip with limited spaces. Everyone in the group who wanted to go (including me) got in, except for Tiffany. She was placed on the waiting list and didn't get a space until the week before. By then, the rooms had already been decided, so the teachers had to move everyone around to fit her in. There was space in other cabins, with people she got along with, but she had a huge tantrum and demanded to be in our cabin. So they removed ME and put her in. I had to go in a cabin with people I didn't know! Then at meal times, she would ice me out and act like I was in the wrong! I'm a young carer, so I rarely get time to hang with my friends outside of school and I was really looking forward to be being on the trip, so I was really upset.
I was a bit cold towards her when we got back to school, but it didn't matter because she acted as if we were all beneath her, she was hanging with Lara now. I wasn't complaining but if she thought she had better friends, she could've not caused all that drama! She's also really judgemental and rude and I've often felt so insecure about myself because of her. So anyway, now Tiffany has kind of left the group. She texted me a week after the trip and she was like "if ur ****ed at me, tell me why" I responded with "no, dw it's fine" bc I didn't want to cause any more drama, but she insisted so I gently let her know why some of the things she did upset me and she gaslighted me, saying it wasn't a big deal and I'm just silly. So she cut off contact with the whole group. And I sort of felt like everyone blamed me and thought that I was dictating who they could be friends with or something which I felt really bad about because I knew that I wasn't but I didn't want them to blame me.
Back to Issy. She was even more horrible to me now for some reason, and when all that stuff happened with Tiffany, she was so silly and said that I WAS overreacting and I drove her out of the group and that I was lying about how I have depression and stuff and I was just shocked!
But half the group seemed to like her and were like best friends, and the other half (me and my best friends) were really annoyed with her!
Fast forward to year 10, we all still sit together but there are clearly two parts of the group - our side and Issy's side. And she just makes me so miserable, she has everyone in the palm of her hand and she has created such a rift in the group I don't think there's any chance of everyone being friends again.
So I first sent an apology last week to Tiffany. Just saying that I felt bad and I'd really like to be friends again. Apparently she didn't accept it. Fine! I just sent it for the purpose of trying to reconcile with her. Then I sent an apology to Issy, saying that I was overreacting and I'm sorry for everything that happened, and I wanted everyone to be friends. She just said "yeah u were a b*tch" are you fcking kidding me?! I didn't do anything to her and it was completely her fault - I obviously didn't say that to her. I just blocked her and I've been so upset since!
That was really long sorry! But help, I need advice on what to do! (Feel free to call me a brat if you think I'm in the wrong, I just want to know what to do!)