If the owner told you no overnight guests are allowed then having guests will risk angering the owner even if there is not a restriction in the lease.
If it was not the owner who told you that you can probably ignore the information. .
No.
Your guests are not irrelevant to insurance; if the landlord is correct, and they broke anything, or anything happened to them, the insurance would not cover them (or your belongings).
If your lease says no overnight guests, and you've signed that lease, then you've agreed legally to having no overnight guests. You risk being evicted if you break your lease.
Re-check the terms of your lease agreement,
If it says no overnight guests,then that is what you must adhere to,if it does not,then you can ignore it.
If your lease doesn't clearly state that you can't have overnight guests then you can have them. It's nothing to do with insurance. Your landlord is just trying to be controlling.
No, you have been told no overnight guests and told the reason why
*allowed