Can anyone identify these books?

I was just reminded that I asked about some books on TV Tropes's Remember That Show... thing ages ago and didn't have much luck (although they did manage to identify one story I read as a kid as one of Joan Aitken's). As a result of which, they've started annoying me again, so I thought I'd see if they sounded familiar to anyone here.
( What I remember about them, such as it is )