Sibling rivalry concern
I have 4 children. Two are on the spectrum two are NT. I find that the kids split into sides and it's always my Aspie daughter and Autistic son vs my NT son and daughter. I know it's normal for kids to form alliances, I recall doing it as a kid with my sister, my concern is really that the alliances are made in that fashion because my NT kids are intentionally ostracizing their brother and sister. Has anyone else experienced this?
My NT kids used to gang up against my AS daughter, but this was prediagnosis when they had no idea why she was acting differently than they were. Now that my son moved out and it is just my 14 year old twin girls, they get along rather well, particularly since I have realized that my AS daughter is prone to tantrums, not meltdowns and if I call her on them, she usually stops pretty quickly.
I have two NT kids- oldest and youngest- and my AS son is in the middle. Honestly, in our family, the AS son is somewhat of the "glue" between the other two. They often follow his lead in play and they get along really well. Once in a while, oldest son will complain that AS son is annoying him (usually with repetitive phrases or when AS son gets angry about terms like "literal" used incorrectly, etc), but that's not very common.
My kids are pretty close in age (18mo between them, 3 yr and 1 day between the oldest and youngest). The worst fights (which are rare) tend to be between the two NT kids. My kids have grown up having to share and share alike, including sharing rooms (for a long time, it was all three in one room) and sharing treats and toys. I think that has helped them bond well.
I have one on the spectrum and many NT (although most with ADHD and/or anxiety). I find the alliances shift all the time. Before dx, the Aspie could get annoying, and it looked like her older sibs were picking on her slightly more than most older siblings pick on younger ones. After dx they understood her better and gave her more leeway, however once in a while the others find I take her side in disputes. If I can stay out of it and trust in their basic good intentions, their arguments can serve as good social skills lessons for her. But I think my tendency to step in and explain why she is acting a particular way makes me miss things. This summer a problem between two of my other kids had to get pretty intense before I even noticed it. That's certainly not fair to them.
Have an only child and grew up with one brother, so my 2 cents may be worth less, but don't kids normally choose the sibling with whom they have the most in common? For instance, if you had two jocks and two bookworms, wouldn't you assume they'd pair off that way? Not trying to discount your concerns, just offering a possible benevolent interpretation.