Generally, you are going to have to assemble/unfold the antenna in the attic. The attic will need to be large enough to allow the antenna to be aimed properly. Measure carefully. Then you're still taking the chance that the attic may or may not be a useable reception location due to penetration losses and/or signal reflections.
Attic or outdoors, try with no preamp. Make your first tests and aim adjustments with only one TV connected (to eliminate the losses caused by splitting). Then, when you know what the antenna actually delivers, you can assess the need for amplification.
Based on the frequent questions asked about amplifiers, it seem many people have the mistaken idea that an amplifier is a substitute for an antenna, or that it can improve the performance of an antenna. Both notions are false. An amplifier can only 'push' signal through losses in cable and splitters attached to the output of the amplifier. Amplifiers also add noise and distortion to the signal, over and above that which was in the air.
If you prove the need for amplification, and are mounting everything indoors, the Channel Master CM-3410 is a very good distribution amplifier that is hard to overload and also has decent noise/distortion performance. It can be powered remotely if needed.
http://www.amazon.com/Channel-Master.../dp/B001FY0B90,
http://www.amazon.com/PCT-Inserter-M.../dp/B005Y12UH6