You probably don't want to use the amplified version of the indoor antenna. The strongest signals on your list have the potential to overload the built-in amp. You would be better off using the non-amplified Terk HDTVi (not HDTVa) version of the antenna.
Installing the antenna in the loft may or may not be necessary. You can try it from your TV area first. If it's not stable enough, then you may need to move the antenna further up.
Just so you know, indoor antennas are always influenced by a lot of random factors. There are unknown objects (ducts, plumbing, wiring, stucco mesh, people walking by, etc.) that can reflect, absorb, or interfere with your TV signals. There's no way to know exactly how your indoor environment will be affected, so there's going to be some trial and error involved.
Attic antennas are usually influenced by fewer obstacles, so they are usually more reliable/predictable. Outdoor antennas are the best because they have the fewest obstacles/random factors.
If you are concerned that your landlord might take issue with you installing an antenna on the roof, you may want to read up on the FCC's rule regarding over the air reception devices (
http://www.fcc.gov/mb/facts/otard.html). It basically says that everyone has the right (with a few special exceptions) to install an antenna for OTA reception purposes. Since this is a federally set policy, it carries the legal force to supersede any landlord, HOA, city, county, or state regulations that try to limit your right to install an antenna.
I do not advocate creating any friction between you and your landlord, but sometimes it helps to know that the law is on your side in this matter. We're just trying to help everyone get the best, most reliable reception of free TV that they can get. If an indoor antenna isn't quite good enough, then an outdoor antenna is the next logical step.