You said there was testimony indicating that they hadn't locked their doors. Where is that?
Laura's door was indeed open, but since RF had MK's keys and RF was the rent collector, maybe she was the "Leader" in the house who had those keys and therefore had Laura's key to open her door.
RF's door is of course opened because her room was broken into through the window. RG opened that when he broke in and came into the house through her room.
I openly admit I have no proof of my theory, just inferences from the crime scene, which I've already stated in detail. But if you can't refute it with fact, it remains a possibility and becomes reasonable doubt.
Where is your confusion coming from?
1. Filomina arrived at the house and Meredith's door was locked.
2. That door was locked with a key
3. Police wanted to enter that room.
4. NO ONE had a key for the room
5. Filomina insisted that police break down that door.
6. If Filomina had a key, why didn't she use it?
Filomina's bedroom was unlocked
1. Amanda arrived at the cottage and did or did not see the broken glass (depends on whether you believe Amanda or those Amanda spoke to after the murder was discovered)
2. Raffaele arrived at the cottage. Filomina's bedroom was unlocked
3. Filomina arrived at the cottage and was not surprised that her door was unlocked. She did not say that her door was locked and there was no discussion or testimony from her claiming that her door was locked.
Laura's bedroom was unlocked
1. Laura's bedroom was unlocked when everyone arrived at the cottage.
2. Laura has not testified that her door was locked and there has been no suggestion from Laura that she locked her door.
Amanda's bedroom door was unlocked.
1. Again ... no testimony to the contrary.