So, I'm going to add a bit of a different perspective.
Firstly, I'm a social worker, not in fostering but have worked with a number of fostered children. Foster care is a last resort, though not the last option,which is a children's home, regardless of what your will says - the state will try and find familial carers in the first instance, and only if they refuse would they go to foster care. Sibling groups are kept together where possible, bit if not possible, they will be split up and may be far apart. Where possible they will remain at the same school, but there's a max distance on travel time before they're put in new schools. Family relationships are prioritised and maintained as significantly important.
Foster care is a necessary evil.
My second perspective. I'm legal guardian of my late best friends 3 children. Her husband died suddenly and she succumbed to cancer about a year later. I had threads on here about it at the time as I was very much in two minds. We've considered adopting them and did get quite far in to the process, but decided against it after some family counselling - we will adopt them, gladly, if they want us to in a few years (they're 11, 8 and 5). I won't pretend it has been easy. We have 2 biological children as well. And we've sadly had to change all their schools (they were all in private, and whilst my friend left sufficient to meet the ongoing fees, the application of VAT meant it was untenable. They settled well in the new school though and we're now looking at secondary for the oldest (the 2 oldest are the same age).
The situation came about because my friend was really upset after her husband died and was worried about what would happen if she died (her health was fine when she said this) and I flippantly said, don't worry, they've always got a home with me. I never in a million years thought it'd be needed. She had a sister abroad but her husband was reluctant and SS deemed them unsuitable anyway - this was decided close to the time she died. Her mum was alive at the time but had her own health issues - she still sees the children now and her health is better.
Overall it's worked well. They're obviously scarred from losing both parents in quick succession and I expect trouble in teenage years. SS have been pretty useless and I don't expect more support if they need it. Thankfully my friends will and personal circumstances have meant the children are well provided for - it wasn't the deciding factor in them remaining with us, but it's definitely helped.
I don't regret it and I wouldn't change it if I had the conversation again.
So you never know!