If you haven't all ready, use your key in every door lock there is..........including trunk. Cycle it from lock to unlock. This should turn off the alarm because they may have knocked something in the door they were working on to get into the vehicle.
Alright, then you'll need to remove the drivers door panel in order to gain access to the alarm disarm switch that was likely knocked out of place trying to get into the vehicle.
The disarm switch attaches to the back of the door lock cylinder.
There is a fuse box at the end of your dash.
Fuse #8 is for the horn.......you can remove that fuse and the horn will stop.
No, the alarm is an integral part of the vehicle. It is an anti theft device so it cannot be disabled or the car thieves would simply disable it and it would be pointless to have it in the first place.
What you need to do is repair the problem with the alarm system.