As far as what counts as evidence of landlord-tennant relationship: it depends on state. A lot of things in law depend on state of course but I'm saying this one specifically because my state happens to have really low standards for what constitutes as being a legal tenant with rights, and I have a personal story with it.
My state, having a piece of recent piece of mail like a bank statement or pay stubs (I believe the time limit for "recent" was something like within the last 30 days) sent to the address counts as proof of residence, you don't have to be paying anything towards rent or bills to have tenant rights.
My mom tried to kick my heroin addict brother out. Now, before I get into what happened when she tried to kick him out, I need to explain why the fact he's on illegal drugs does not help in getting him removed from the house.
He's in this cycle where he just keeps relapsing and getting in legal trouble then going to treatment rinse repeat, and every time he's in between "gets in legal trouble" and "goes to treatment," there's a few weeks in between his trial and the treatment centers having a bed ready for him that he treats it as legal limbo and goes nuts with the drugs.
No extra drug charges (for the same drug you were initially caught with, so long as it constitutes a personal amount) get brought in after the trial/before treatment starts.
Treatment doesn't start for a few weeks after the trial because treatment centers are so full unless you're paying for private.
Before the treatment center will accept you, you have to go to detox center.
To go to detox, you have to actually be detoxing and in need of medical supervision (heroin detox can kill you). There's a time frame here with detox, the first part isn't the dangerous part, it's later in the process that's dangerous. Detox center will turn you away if you are still just on your first day. You gotta self detox a little bit until you're dope sick and they'll accept you.
Unlike treatment centers, detox centers keep people for less time so there isn't a wait. If you get into detox but there's still a few more weeks until the treatment center has room for you, the treatment center won't take you because it's meant to be for people just out of detox.
If too much time passes between detox and bed availability for treatment, the treatment cente Will no longer consider you as qualifying for treatment because the heroin treatment center is meant to come after detox...
So you can't just detox on your court date then get into treatment a few weeks later.
It's just expected that you'll keep using just up until right before the treatment center has a bed ready for you.
It's an absolute mess of bureaucracy, but this is why my mom couldn't just call the cops and say someone has drugs in her home.
The courts know he uses drugs and accepts and expects that he's going to use up until the treatment center they're sending him to opens up, they're not gonna add more charges for him using the same drug. If he gets caught with a different drug, then they'll stick it. Same drug, no point. At one point he had charges for both meth and heroin, that was a crazy time but I don't remember how that played out legally.
Anyway.
She wanted to kick him out cuz his drug use is getting extreme even for him cuz he knows he doesn't have to pretend he's not using, and he's acting like an absolute shit cuz drugs just make you terrible and obnoxious.
But he had mail. Court papers that were sent to our address.
She wasn't even allowed to kick out my brother's heroin addict buddy when he came to visit, she was told my brother is a legal resident and he's allowed to have guests if he wants.
She would have need to served him a 30 day eviction notice to get him out just because he put her address down on an official document. In the end it was easier and faster to just let the court mandated treatment get him out first, and make him send his mail somewhere else.
Obligatory IAMAL, this is just what I witnessed as a young adult when my mom tried to kick my brother (and a few weeks later his guest) out of her house I was also living in. The system isn't perfect and cops sometimes are wrong about what they can and can't enforce and why. But I've definitley heard of other horror stories from states with squatters rights and things like that and just wanted to share one of my own and what bullshit that all was.
Sorry for the long ass story, I may still be somewhat bitter about having to live with an addict at 17 and no choice in the matter just because he was a legal tenant just for having mail sent to the house, but I got kicked out a few weeks later when he came back to live with us even more hopelessly addicted to both meth and heroin this time (idk why my mom let him back) but I had to leave cuz I was "starting things" with him and I was "causing problems" by voicing things like I need to take a shit and you've been in there for 2 hours doing your junk so get ouy, or calling him out for taking light bulbs from around the house to smoke meth ouy, or stealing my change collection, or any of the endless list of other obnoxious selfish things drug addicts do, but I was barely 18 and had no official documents from the last 30 days so I was not a legal tenant so it was legal to kick me out with 2 hours to pack my shit and leave with no place to go. Tenant laws can be stupid.