How I am handling a terrible situation

I'm currently renting out a basement unit of a duplex. Upstairs is a family with kids and beside is 2 brothers in another basement unit.

What I'm currently experiencing is right out of a bad movie.

The upstairs family:

• We are both new to this duplex, they moved in a month before I did.
• A few months into our tenancy, the upstairs neighbours started accusing me of smoking in my unit, mentioning a smell of herb or marijuana.
• We share a connective staircase and supposedly the smell and smoke is coming from there into their unit. I'm a non-smoker and I do not use marijuana or do any drugs.
• At first he stopped me on the street to talk to me about it and I had no idea what he was talking about. After thinking much about it, I still could not arrive to a viable conclusion.
• I've asked them to notify me next time there is this smell and smoke.
• About a week later he knocks on my door saying there is a "very strong odour".
• Lucky for me the landlord happens to be around.
• We all go to investigate the staircase and the landlord and I are baffled as there is no odour nor smoke. The neighbour couple are adamant there is a strong smell and a lot of smoke.
• Their kids say in the background "There's no smell", disagreeing with their parents.
• I would've invited them into my unit, but I felt no need to prove anything to the landlord as he was obviously agreeing with me.
• I politely but firmly tell the neighbours, they need to stop making false allegations.
• Afterwards, the landlord and I have a conversation about them probably being not right in their heads.
• A couple of weeks later every time I open my door a loud alarm goes off for 5 minutes.
• I knock on their door and they have no idea what was going on either.
• We have an out-of-service alarm system and I ask them if they touched anything on the pad.
• First they say yes then they say no. I keep getting conflicting answers each time I ask. I must have asked them if they touched the keypad about 10 times.
• I still have no idea what they did or why it was my door that was activated.
• The wife accuses me of doing drugs in my unit during this brief exchange. I am pretty annoyed at this point.
• I contact the landlord but he is away. Something must be done ASAP as it's driving everyone crazy.
• I leave a note through the door saying I need to go into their unit and disable the alarm (I figured it out on youtube).
• I go in and disable it, we are happy there is no more blaring alarm.
• A couple of days later he knocks on my door and complains I am smoking in my unit again, says there was a smell the night prior.
• I invite him into my unit and he agrees there is no smell in my unit.
• I tell him I want to get along with them and they need to stop this or have evidence I am smoking in my unit for them to say this again. There wouldn't be any because I am not doing it.
• About 2 months later he knocks on my door and says I was smoking in my unit the night before.
• I am fuming at this point.
• I basically tell him to fuck off.
• I write a letter to my landlord saying if these neighbours make another false allegations against me, I will strongly consider legal actions. I also request them to ask the 2 brothers who live in the unit next to mine (although I didn't warn them of this).
• The landlord says he will talk to them.
• I hear them talking upstairs that night.
• I also hear them talking to the 2 brothers beside my unit.
• The allegations have stopped thus far.

The 2 brothers in the unit next to mine:

• From the night I moved in, they could be heard screaming in excitement and disappointment. I figured out they were playing video games (and I was right).
• The walls are paper thin and the screaming is almost non-stop and occurs as late as 1am.
• I try to let go, but by the third night I am losing it so I go knock on their door.
• I find out they are playing video games and they are really into it. They apologize and says they will never do it again.
• To their credit they were quiet for a while, but I would still hear them every now and then. Overall nothing too awful.
• The relationship isn't too bad, I even tell them the upstairs neighbours are accusing me of smoking. I ask if they ever smell something or see any smoke and they are just as confused as I am as they would be the first ones to smell drugs and see any smoke.
• Around the time I disabled the alarm upstairs, which happens to also power the door bells, they progressively start screaming again.
• I knock on the main door and the door through the laundry room located in the middle of the units, I get nothing. They are probably wearing soundproof headphones while they do this.
• I end up leaving a note asking them to stop screaming.
• The next day they knock on my door and apologize again.
• They offer their phone number for me to text to remind them to be quiet when they are being too loud.
• I politely refuse, remind them I can hear everything that is being said in their unit and for them to keep that in mind.
• They are dead silent for 2 days.
• Then they start screaming again.
• I leave another note through the laundry room asking them to be quiet.
• They are dead silent for another day.
• Then they start screaming yet again.
• I am pissed.
• I knock on their door for about 10 minutes and get no answer.
• The next day they knock and ask if I was knocking on their door.
• They are pretty defensive this time and say they are trying to be quiet and it was only about 9pm when they were screaming the night before.
• They also mention they are screaming because they have been losing in their video games.
• I remind them I can hear everything that is being said in their unit, so I can of course hear the screaming. Furthermore, I suggest since we have a problem in this house with the lack of noise barriers, we should adopt to it rather than to ignore it.
• They offer me their phone number again as a temporary solution.
• I take it and text them 10 minutes later when they are being loud again.
• I warn them if I have to ask them 3 more times, I will have a talk with the landlord and report this problem to the city.
• The bylaws in this city are on my side; if I can hear them screaming at any time it's a problem and the city officer will make a visit to them to warn them. For every repeating visits they are fined.
• Around the holidays they are screaming, but I try to let it go in holiday spirits.
• The other night at 1am I text them I am trying to sleep but cannot since they are screaming.
• They apologize, tells me they didn't know what time it was.
• They have struck twice so far out of three.
• Although they have vouched for me on the whole weird drug accusations coming from the upstairs neighbours, I will probably report them if they continue screaming.