If I use a lighting spell on two buildings at a time (both buildings in it's range), how much damage will the spell do to each building. Assume if the damage is 100, will the damage be 100 on both buildings or will it be divided say 50-50?
The lighting spell is most powerful at the center, but further out, it is random how the hits are distributed. This means that it might give a lot of damage to the right side of the center, but very low at the left - or some other distribution. You really wouldn't know. If you want to make sure to give the most damage to one prticular building, you must ensure that you center the spell on that building.
If you center the spell exactly between two buildings (for instance a mortar and a wizard tower), you can get lucky to take out both with 2 spells, or you can get unlucky, and take out none of them (just weaken them).
The farther the spell hits from a building's center, the less damage it deals to it. So, the damage won't be 100%, but higher than 50%.