I need to have multiple antennas connected to my module, what do I need to know about multiplexing to get say 4 antennas connected to a single module?
And can somebody recommend me the hardware needed, preferably something I don’t need to solder together entirely from parts 
You will need a reader that’s capable of 4 antennas. Something the the below would work.
Not going to happen with the SparkFun reader, at least not without soldering and some programming ability.
Really? I was under the impression that the reader itself wouldn’t care if it receives antenna signal from 4 different antennas as long as something else handles the multiplexing and makes sure that at any point in time only one antennas signal is passed to the reader 
As far as I have understood the board does support multiplexing with up to 16 antennas (the GPIO 1-4 is used for that).
I don’t mind soldering and also coding to some extent, but if it’s not supported by the library provided by you guys it’s of course at lot more work to be done 
I’m afraid I’ve spend quite a lot of money on something that in the end will no fit my needs with this board. This of course is on me for not having done my due diligence in the first place, but none the less it’s really a downer
You might be able to add the additional lines of code needed with a few hours research on how variables work and how to use timing/delays (or whatever method you’d like to control the switching schema)