Unless you have some awesome insurance. If someone get injured jumping on that trampoline. You will have to pay out of your pocket. Most insurance will not cover them. I would start with a notice to inspect. Sounds like there is enough problems in the yard to get started. Everything comes down to what your lease states. If you have language that you can repair issues and add it to the rent first. Then you could follow up with evicting when they refused to pay the next month rent.
I would call the city to have the vehicle sited for being un-registered. Then demand it be removed or corrected. This city violation could give you more ammo in court in getting the T evicted.