:'(unfortionately tanks do not fire on anything tha tis not an enemy unless it is an accedent, even with the dofire command.
I have had the same experiance with an invisible Hpad, trying to simulate an airstrike on open ground where enemies are reported to be present, kind of like vietnam.
What I did here was I had a flying UAZ with a loop setpos, and when the chopper ran out of rockets, the UAZ deleted itself. The chopper never hit the UAZ because it was setting its pos faster than the rockets could fly, so therefore the rockets hit the ground. With playing and experimentation, I got it right.
I suggest for the house, you have an invisible marker, and unitcreate an enemy soldier at this marker which corresponds to a position inside the house, this will take experimentation to get right. Reveal this unit to the AI tankers. He will fire on this unit and should destroy the house along with the soldier inside. Delete the dead soldier after the house is destroyed. What were doing here is making an accedent that simulates an on purpose.
If it is a house you can't go inside, maybe you could try something similar to what I did. If the UAZ, or whatever will look bad, then make a cutscene out of it, and point the camera away from the UAZ, or whatever.
Destruction of towns and houses seems like a good movie thing.