Depends on the amp. If you have a typical 2 channel amp that is stable into 2 ohms(4 ohms bridged) wire the voice coils in series. That will give you 3 12 ohm subs. Wire these in parallel and that will give you a 4 ohm load.
If you have a mono block amp stable to 1 ohm just wire everything in parallel and that'll give you a 1 ohm load.
i have a 1 ohm stable amplifier only brigeable with slave amp 2000w 900 rms what do you recomend should i change the amp or ad another? or should i just add another woofer and use both channels?
i don't know, from what i'm getting, your amplifier is stable at 1 ohm? so yeah, you can us all three subs and wire them all down to 1 ohm, just like fishy said.