Since no other member has commented, I will give my opinion, although from quite a distance in West Texas. First, I am envious. You have access to all of the major networks including the more minor Mynet and Ion. They both have great repeats of recent series in HD. You do indeed need a high band VHF/UHF antenna, especially since both of the ABC affiliates are on VHF. I would get something in the midsized range if used in an attic as the structure will block about half of the signal compared to outdoors.
I too would want both the Raleigh and Jacksonville markets. However, simply combining two antennas with a splitter/combiner is never a good idea. It has been known to work, but I have never seen it in my 40+ years of experimentation in 5 different cities. The problem is that antennas are not 100% directional. Although the most signal will come in through the front of the antenna, signal is also recieved on the sides and back. Let's say you have antenna A pointed at city A and antenna B pointed at city B. Some signal from city A will come in the back or side of antenna B and mix with the signal from antenna A. Since antenna B is a few feet further away and the cables are probably of different lengths, the two signals from the same source will arrive at the tuner at different times. In the analog days, that would cause a "ghost". With digital it just causes mixed information that can cause drop-outs or even loss of signal.
The proper way to get signals from two different directions is either to use a rotor or have separate antennas on a switch. Rotors are of course inconvenient, but have their uses. Switches at least are fast and durable. There are special order devices for adding one channel from one alternate direction in with the others, but you have too many channels from both directions for that.
To keep things simple, I would start with one antenna pointed at your slightly weaker JAX stations and try to take advantage of the fact that the Raleigh channels may just come in off of the back of the antenna. Since you will be in the attic, it should be easy to fine-tune the direction of the antenna and try and maximize the signals captured by one antenna. If you find that to be unsatisfactory, you may then consider a rotor or switch and second antenna.
Hopefully, some other members will chime in with more suggestions. Feel free to ask more questions and let us know how it works out. Best of Luck from Texas.