It does seem that fire safety is completely in conflict with anti-break in security.
Fire safety says no keys to get out
Insurance says must use key operated lock so that a burglar can’t either reach through the letterbox, break glass in the front door and reach in, or just slip the Yale lock with a credit card or strip of packing plastic (which is really easy to do),
I get your landlady’s point – a good number of burglaries happen over night when people are home and with a number of your sharing the front door opening at odd times must be fairly common.
One option would be key operated bolts like this. My parents have these at the top and bottom of the front door and leave the key in them. No way you could reach from the letterbox (though don’t stop a glass break). Of course, once they’re locked someone outside cant’ get in (same problem leaving a key in the lock). In our last house we had face mounted bolts (something like this) but our lodgers locked each other out a few times (how do you know everyone else is home when you get back?)
I reckon the best option is a deadlocking NightLatch can’t be tripped with a card or plastic. and some sort of flap on the letterbox to stop people reaching through.
My mum has Alzheimers – last time I was there she’d locked the front door and lost the key. Only other exit would be via the kitchen which is most likely place for a fire to start. I wasn’t happy at all.