I think that the older child is always of benefit to younger children and my days flow better during the holidays when I have the older children. Even that after school time is calmer than it should be with that many children.
Of course there are individual children who don't help the atmosphere - but that is often due to particular issue rather than the situation. I have had to let a few older children go - usually they were unused to boundaries
Yes I am Norwich way - but if it works, you never know I might be able to talk on Woman's Hour about it