control 2 or 3 antenna with 1 reader

you will typically want to use a commercial system designed to do this kind of application rather than build your own. if you do decide to build something, the one thing you will need to do to get good coverage is detune the antennas that are not in use. simply switching to a different antenna and leaving the "disconnected" ones as-is will sap energy from your active antenna's RF field.

i'd suggest spending a little cash to get a commercial reader that supports more than one antenna. these multi-antenna readers work by powering up only a single antenna at a time, and detuning the others, then cascading through the connected antennas in quick succession.

but, if you want to figure it out for yourself and you don't have any electrical engineering under your belt, searching patents is a good way to start... they usually explain everything you need to know, and include diagrams, schematics, etc. another place you can look is google images.