It IS neglectful and given what you say about the children "never complaining" I'd suspect that's either not true or there's been worrying consequences if they did that have deterred them from doing so again.
This is NOT a healthy or supportive environment and frankly you should be reporting to the appropriate services.
"The 11 year old isn't expected to look after her sibling's" yes she is. She shouldn't even be asked at this age it's far too much responsibility.
If you're not talking about your own parenting then I think it's also entirely possible this isn't even the worst of it! How "secure" the home is irrelevant, there are other dangers than "stranger abduction" which is incredibly rare anyway. This set up makes them more vulnerable to those who ARE likely to take advantage as they will know the family and have their trust but also know there's little to no adult supervision, plus there's the other dangers of fire, broken glass, falls etc which an 11 year old is nowhere near mature enough to deal with the responsibility of. I don't doubt the 11 year old could follow the right actions, but any accidents that happen, particularly any that lead to lifelong consequences they would likely forever blame themselves that's a horrifically huge burden to place on a pre teen that could potentially wreck their mh long term.
Having an adult present isn't just about the children's physical safety, it's emotional reassurance and supporting their emotional development. Who is listening to their worried before they fall asleep? Are they eating properly? Are their hygiene needs being properly met? I highly doubt it under this set up!
This is your mum and siblings you're talking about? Honestly? I'd tell mum to cut this crap out or you WILL be reporting her and mean it. That's what I'd do.
"What would they do? From peoples reactions its sounds like they would be immediatly removed from her." That's actually unlikely. Particularly with the cuts (it's very expensive to provide care for children) plus their aim is to keep families SAFELY together. Sadly even pretty horrific cases of blatant abuse don't even always result in removal of children.
Instead (and I'm not an expert) they'll likely be assigned a case worker who will talk to mum about what IS acceptable parenting, help to access resources to achieve this possibly including community connections, parenting classes, mh support, financial support if needed (they'll help her make sure she's getting all help she's eligible for and possibly help from certain charities if it's deemed necessary), perhaps counselling for the children, I'd have thought particularly the 11 year old...
But as I say I'm not an expert. I'm just a single mum who's had serious mh issues which have meant when dd was very little it was felt a good idea to give us support as a family from SS. My experiences were very positive, even though I had dreaded it.
"Kids are always properly fed and washed" by whom?
"All doing well at school, mum always helps with homework and has intervened when there has been any issues." Guessing this is based on what your mum has told you? Because the school won't be speaking to you.
And yes it is pretty terrible, you're just too close to see otherwise particularly if your childhood was even worse. And I speak as someone who had a pretty shit childhood themselves.
How is the 11 year old getting home from the after school club?
In what way was your childhood worse that you think isn't happening now? And why do you think it's not happening?
"This makes me especially sad. It’s well behaved kids that are often ones to watch, they don’t feel safe enough to express themselves" this was me and my siblings. We got teased/bullied for being "goody two shoes" but it was both self preservation and protecting mum, cos if we'd been naughty at school or with anyone likely to say anything to dad that would have risked our safety and pretty much guaranteed mum another belting! So we were quiet, well behaved, hard working students (woe betide we got less than a "b" for effort on school reports).
REALLY happy confident children WILL play up on occasion. They feel safe to do so.
Op please support your siblings to be better cared for.