Are you suggesting that it's a better idea to just slide them in with the special ed kids and give up altogether on them ever achieving their full potential? They are all capable of achieving GCSEs. They deserve the opportunity to do so.
Good schools can and do support a very wide range of academic abilities without putting children in a classroom with children two years younger than them.
They also regularly support children who've missed large chunks of school. Imagine a child returning to school after missing months with a serious illness and being told they'd got to drop back a year because they hadn't kept up in hospital. It doesn't happen. They'd be supported to catch up as the Ingham girls should be.
IME, sometimes, kids will be dropped back one year, often if they've moved from another country/a totally different education system later in high school, but never without the family's agreement and certainly not when it'd be 'social devastation' for them. I've never come across a child two years out of year.
Also, I was definitely not advocating giving up on children with additional needs. Plenty do get good qualifications. My point was that the average school will be catering for children who could do all their GCSEs at 14, children who would be thrilled to get a couple of level 1 qualifications at 18 and everything in between.
Remove the YouTube element and the Ingham children aren't anything the average school won't have seen many times before.