Sibling relationship awful - one with suspected ASD

[Mydustymonstera]

Anyone able to help me talk through struggles my 2 daughters are having? I am managing this really badly it feels.
oldest is 12 and awaiting assessment for ASD / maybe inattentive ADHD. Very sensitive, quiet, strong sense of justice, prone to aggressive meltdowns with swearing, used to be physically aggressive but less so now, needs a lot of silence and space, creative, massively caring and huge sense of empathy but struggling to feel this for her sister…

younger is 8, boisterous loud and silly, very tactile loves hugs, if upset can be jollied out of it, gets excited, talks all the time, wants to play with her sister, can flit from one thing to another easily.

if I’m not on them constantly then younger gets overexcited and talks loads, older gets more and more tense until there is something where the game is wrong, she hasn’t listened to her, touched something she shouldn’t have etc etc until older has meltdown.

older one feels I don’t love her and always take younger’s side. But she gets so extremely irate at the smallest things from younger and can escalate so quickly to shouting at or even pushing her so of course it’s always her im shouting at to stop first…
tonight she talked about how she feels and I just feel awful. I cannot go unjustly or excessively punishing younger for actions which are natural. Also it wouldn’t help!! But she feels utterly unheard.

she also doesn’t think she has ASD ‘I’m just weird’ but she says it in a happy way.
any advice????

Is the younger one being assessed fur ADHD too @Mydustymonstera?

No, not been pursuing that. She has some traits but it’s not getting in way of her ie concentrating on her learning, playing with others, sleep etc. only relationship she has trouble with is with her sister!

It sounds like they naturally have conflicting needs and styles, so they need some help on 'rules of engagement'. We have a similar situation, and it's really hard to try meet everyone's needs and a reasonable number of their wants!

Does oldest have her own room or other space she can retreat to? Could she (with support) work on recognising when she's nearing her limit and ending the game before she hits that limit (most of the time), so she can go get some space and recharge? Especially for the situations where youngest really isn't doing anything wrong, she just wants to chat whilst eldest wants quiet.

Equally, if youngest is being very boisterous or loud in the main living space, can she be redirected somewhere else to burn it off? Would a small indoor exercise trampoline help? We also say things like 'it's fine if you want to continue making that noise, but the rest of us want to be able to talk, so please go play upstairs/into the kitchen/whatever until you're done'.

Similarly, you say youngest is very tactile, but eldest needs space. We have a very firm rule that if one person says they don't want to be touched or want a little space, that must be respected (but if you're at the point where you can't cope with someone on the opposite end of the sofa, you need somewhere more private – you can't generally take over the family space).

Are there types of play that work better for them? For us, it's board games/card games and building with magnetic tiles or lego, so I try to focus interactions on those, and steer them away from things like imaginary play unless tolerance seems particularly high.