First don't feel bad, you are doing your best and listening to what your children say they need and putting their needs first. Getting through school is hard it is not a given that mainstream school is right for everyone.
I have (nearly) got 2 autistic young people through school. DS is 19 and at uni, DD is 17 and just started y13.
DD has had a really tough first day. She had a melt down on the way into school and so DH brought her home, then got her back in for 10. Then DD calls me at 2pm in tears I talk her down for 40 mins. Then DH picks her up again! But that is a pretty typical day at the beginning of term 😅 I hope tomorrow will be easier for her and us.
DS was very determined and academic so he powered through school on force of will. Got excellent results despite various barriers and sensory issues and needed very little additional support just acceptance that he is autistic will not be flexible, will need warning about changes, won't do well in group work and needs extra time and a scribe for exams.
DD has an EHCP, needs more support, medication for her ADHD, safe space in school. Help with her anxiety and she needs me and her dad to be there for her. She is constantly worried about what she ought to be doing, thinks she is being judged all the time. Gets very stressed and her meltdowns can be epic. So school has been a challenge! But she is predicted 3 As and is a clever old bean. So I am a bit terrified of her going to uni and how that will work.
My kids got/are getting through school because ultimately they want/ed to be there. Despite the struggles, and the social pressures. They were/are distressed by other kids not following rules or perceived injustice if teaching staff are unfair. But they want/ed to get the qualifications and that keeps them motivated.
Every child will have their own motivations, priorities and ways of coping/ learning some will not be compatible with school. There are other places and ways to be educated/ get qualifications, progress and develop. The UK is pretty narrow really in how education is perceived and structured.