There are a few good answers here. You should begin by determining what bands the channels you want to get are on. See how strong they are using the meter, or by the online signal websites out there. Assuming you have a few on Vhf, and some on Uhf get the biggest antenna you can have for each application. Amplify them separately as needed. You may need to use 2 preamps, possibly an attenuator, and then a combiner and then feed that to a distribution amp, and then a single coax to all yer stuff. I did this with 2 Uhf preamps and a attenuator, and a combiner with one vhf preamp because the UHF channels are the real trouble where I am. But combining 2 antennas trying to get the same channel you may get multipath distortion which will possibly cancel, or degrade the desired signal, But it will also and most importantly add noise! That is the biggest bad for this digital stuff. I have a spectrum analyzer and I did the two antenna thing, and the amount of noise outranks everything good. If'n yer in a real fringe area use good low noise preamps, and distribution amps. Use good cable, ground it to keep the noise down.
http://www.tvfool.com/modeling/ This site is pretty good to see your estimated signal strength and noise margin. And the noise is important, design a good system and you will be happy. SolidSignal.com has some good combiners, low noise preamps of all kinds, and dist. amps, and a attenuator. Using a separate path for each signal V vs Uhf also keeps the noise down cause the amps have band width limits. Also if you use a directional antenna you may have to point it and tune for one of the poorest channels, and let the amps make up for the channels that can afford to suffer when pointing the antenna.