Julia, you can learn to do this.
If you are going to survive as a landlord you must be firm but fair. Have the rules set out from the beginning and then enforce them immediately. Tenants actually understand that there are rules to follow, but they are a lot like 3 year old kids, always testing to see what they can get away with.
Once they test a couple of times and are met with a tough (but polite) response, they will usually stop testing.
Your only power over the tenants is your ability to evict. Use it wisely.
My rental agreement sets out how many days they can be late before evicition (it is state law), and they receive their pay or quit the very first day that I can post it. Normally, one pay or quit, posted the very first time they try to pay late willl straighten up the rent issue and they will pay from that point on.
Your rental agrement should state how many cars are permitted. If it doesn't, you are probably out of luck and need to rewrite your lease. If it does, then you send a written notice that any cars not on the lease must be parked on the street.
Or.... you are permitted to make minor changes to the lease. Notify all the tenants (30 day notice) that there have been too many parking issues and you are going to assign parking spaces.
Assign the spaces and post signs that violators will be towed THEN DO IT. A couple of tows and your tenants will be trained not to park in someone else's space.
Instruct your other tenants to start calling the police about every loud party. Then you can send a written notice to your problem tenants that you have received a complaint from the police and they are to cease with the loud noise immediately. A couple of police reports and you will be able to evict them (in most states)
I only do month to month, just exactly so I can get rid of tenants like yours.
One last thing-- very careful screening will keep the majority of problem tenants out. These guys didn't start ignoring their bills, having loud parties, and parking all over the lawn only after you rented to them. careful screening should have caught them before they moved in.