Per Rabbitear.info not all of the close in transmitters are on the air. Still, strong local signals will pose a problem for most, if not all, amplifiers.
Take a look at the dimensions of the
Winegard HD7698P. It's long, so I don't expect it to fit in most attics.
The problem I see is that you will need to rotate an antenna to be able to access a full line up of the major networks and, in the attic you will need every bit of gain you can find in an antenna if you are going to have a reasonable chance at receiving the weaker signals and then have enough signal to split to two sets. Again, you're in a spot that makes me work hard to avoid the use of any amplifier.
If you could mount outside in the clear, you would be able to use a bit smaller antenna, but without an amplifier the big Winegard is not overkill, IMO.