I've hesitated to say this, but when I worked in secondary schools there were clearly some foster carers in our authority who saw caring as a money making enterprise.
My husband was surprised when he was told that foster caring was what someone he knew did for a living - both the young woman her mother were foster carers. (This may not be the case in other areas, of course.)
The vetting only goes so far. I recall my incredulity when I realised that the foster parents of one of my pupils were the parents of a former feral pupil and that the girl being fostered was having to share a home with this now grown male.
I did meet many wonderful foster carers and also many wonderful kinship carers.
My understanding was that foster care was only ever a last resort, when there was no other family or the family was unsuitable.
I have very fond memories of an older couple who fostered a child who was on the spectrum. The child was one of a large family where the mother - also on the spectrum - had been unable to look after her children properly and had physically abused them.
The children had been split up and sent to various institutions.
The foster carers managed to trace the eldest sibling who had physically protected the youngest by hiding the child under a bed and taking the beatings intended for the youngest. The eldest was living independently by then and once contact was re-established the two had regular meetings.
I'm wittering on here, but just to say that I admire the fact that you're making preparations for your children even though they probably won't be needed.
If it were my child, and there was a family member who seemed to be of reasonable character and they were willing, I'd choose them over a foster carer.