@Fluffycardigan
The fact you know, acknowledge it and are trying to change it is a massive thing in itself.
I'm afraid the reason I think I explain it so well is because still very recently I've been the adult child living at home. I don't know about reading material but maybe just some active thinking.
Have your children lived away and come back? Maybe at uni?
If yes:
Think about how many nights out at uni they've been on, which you had no idea about, and they were fine.
Think they've lived independently and clearly survived that so can easily survive an evening out with friends.
Think that being in a different place doesn't change who they are, you don't police them, where they're going, who they're with, when they're away, why does being at home change that? Answer - it doesn't
If no, it's a little more difficult but you have to remember they're still adults.
You have worried about them for year and everything has been fine, clearly your worry amounts to nothing, concentrate on that.
You wouldn't police any other adults movements, who they've with ect, they are still adults so you can't do this to them.
Remember if any other adult (boy/girlfriend, housemate ect) kept tabs on them like this, asked them this many questions, even if out of concern, you would be telling your child that they are being controlling, and would encourage them to end the relationship. I'm obviously not saying they should end the relationship with you on a one off but if you, another adult, continue to treat them, an adult, like this they will feel controlled and possibly want to distance themselves and you don't want that.
Sorry if this advice isn't perfect, I'm no expert in this. Just some of the things I tried explaining to my mum when she was questioning me going out, keeping tabs on me ect and I found it controlling and interfering.