Amp wiring

I have 2 x 12" 800 watt subwoofers and 2 x 10" 400 watt subwoofers and a 1200 watt amplifier.  Would it be safe to wire all four of these speakers to the one amplifier or should I get another amp.

The impedance rating for the 12" speakers is 4 ohm.  The impedance rating for the 10" speakers is also 4 ohm.  The impedance rating for the amplifier is 2 ohm capable stereo.

I agree you will have a mess if you mix subs, whether using one amp or two, unless you isolate the freq band to each......and then there still is no point.  It looks like you are trying to use what you have available for the loudest sound.  You said that is a stereo amp, so it has two channels capable of 2 ohm.  Each set of subs will parallel to 2 ohms, so each set can go onto a channel.  (Not a recommendation, but just to answer the question.)

Do a search through the forum for questions/answers about mixing sub sizes.