yes you can put the 2 fans together, twist the 2 red wires together and same for the black.you will need to find a transformer that puts out 8-14 volts dc and at least .20 amps (or 200 miliamps)(1000 miliamps = 1amp)
someone above stated you want to match the amps as close as possible but this is not true, you need a transformer that puts out at least as much amps as your fans draw but more is good! a 1 amp transformer will work better because you are only drawing 1/4 of what it can produce so you wont be working it as hard as if you were drawing its max power.