First one I read it in the 90s, something my parents got from the library which was very unsuitable for my age. I've been googling on and off for years but not been able to find it. It's about a group of teenagers (I think UK) who find out that they can travel to another realm if they spill blood under electric lines/pylons. They encounter the devil there (who is described as having a massive erection!) and something bad happens but they are allowed back to their own world. Skip to them being grown up and parents and they yearly and subconsciously do weird rituals to keep things 'safe' like hammering a nail through their hand etc. Their kids discover this when teens and do the blood/electricity thing to confront the devil and finish it.
Second was again read far too young - it was about a series of really grisly and inventive murders - turns out to have been done by a kid who is mute but has a special talent for murders! His mum keeps his mute dad in a cupboard who's only talent is sex!
I was a feral child who read anything and everything.
Tbh, not sure i want to find the second one but the first one was good and i'd love to re-read and see how well i remembered it.
Thanks!