I have a child with ADHD who we have had to parent in a very specific way. He needs a lot of work pretty much every day to avoid meltdowns and keep on track. Especially now he's at school.
We happened to have a 2nd before he was 2, in other words before we really knew.
You definitely have to have different approaches. I have to discipline him in a different way and you would be very conscious of not making the NT child think you were "harder" on them just because you're able to actually lose your rag at a NT child and it doesn't become WW3 for the next hour. So it makes you really be very conscious of how you're parenting both of them and how to have a happy middle. We will likely have challenges with DS the whole way through school and maybe beyond. Dd simply hasn't had the same issues.
On the other hand, they are as thick as thieves and have definitely saved each others sanity through our lockdown, which here was from early March to September. So literally 6 months where they didn't see another child. They are very very close. But then there is only a small age difference. DS is so used to DD that he knows what she likes and doesn't like and doesn't get upset when she doesn't want to do something, because she's never liked x or y.
She has also given him a lot of courage. He is anxious and she always has to do everything first. In the playground, she is fearless and bounds across the jungle gym whilst he watches. And after a few weeks, he quietly starts following her. Whatever she does, he observes like a hawk and its good for him to see that nothing bad happens.
They also can really relax and switch off with each other. They don't have to make an effort. They can just flop and watch TV together. There's a lot to be said for that kind of easy undemanding companionship.
I also think that if we didn't have DD, we'd be much more obsessive about DS. It can be pretty intense, having these meltdowns for the smallest of triggers. But having a NT child there reminds you that he is just a normal child too, and we have to relax. And we also have to encourage independence.
So we think its been very beneficial to him and has socialised him a lot and made him braver. But every child is different.