There’s something about the tone of op’s answers that makes me suspect this thread isn’t genuine but op, taking you at your word, it’s your house and your rules, and if you are not comfortable with your dd having her bf over to stay, then that is your prerogative!
Certainly if you feel you can’t trust your dd and her bf, and you would constantly have to police their behaviour, I would suggest it’s better not to invite him,
Just because something is deemed legal by the state, eg sex at sixteen, doesn’t mean it’s ideal. What’s the rush?
Also, it’s fine in theory to state that your seventeen year old’s sex life is not your business; but it soon would be if a pregnancy arose out of it.
Most eighteen year old’s are not fully functioning adults in many areas of life, so I don’t understand why parents are supposed to support and encourage them to engage in an activity that could have profound consequences on their life that they are not yet ready for?
My view on this is that a family home, especially if it houses younger siblings, is not the most appropriate environment for teens to explore their sexuality and that is better done at university or when they are of an age they can afford to contribute towards, or pay for trips away, or for their own accommodation. Call me old fashioned; I don’t care! My adult dc never seemed too upset about it either.
Having said all of the above, I fail to see what your neighbours have to do with this decision?