You lose at least 1/2 the power in a 2-way split (-3dB), so each line is receiving no more than 1/2 the original signal strength on any channel. The loss through the splitter varies due to a number of factors including frequency. In some cases you may still have plenty of power for reliable reception on all sets. I'd try the passive splitter first (low cost and reliable). Note that cable quality and careful installation of the connectors are also very important to the outcome.
If that passive slit causes too much signal loss (evidenced by increased pixelation and/or dropouts in the A/V) then use a simple distribution amplifier as NightHawk suggested. Each tap on the disti amp will typically have just a slight gain (2-3 dB). You should also terminate any unused taps with a 75-ohm load to prevent reflections...