I'm wanting to connect my 2 turntables via my mixer to my mac so i can share the speakers.
What model of Mac, and what speakers? What about an external amplifier, because your Mac won't have a very high output. Turntables are pre-amp, but your Mac can act as an amplifier.
You'll probably have a 3.5 mm audio-in port on your Mac. From your mixer I'm guessing a 10 mm stereo outlet socket, maybe RCA, perhaps the old clamp or screw-down wire connectors. You'll need a cable with the two different sized or type of jacks/plugs on it, or a necessary adaptor. Griffin and Pudney are two brand names for audio equipment that come to mind right now. There's a large range of audio cables and adaptors.
I also want to use my itunes as a channel on my mixer, I'm guessing this is possible?
Sure is. Either switch the audio cable outlined above to Mac 3.5 mm out, and 10 mm (or whatever) in to your mixer; or have a separate cable for that. You'll still need to amplify pre or post mixer though, or does your mixer have a built-in amp?
Post again if you want any further explanation eg. how my eMac is set up to play via external amp/speakers (no mixer though, and I don't use line in); or how to convert analog recordings to digital for use in iTunes.