Darry,
If you want to sound special then your bandmates need to learn to control their volume.
For rehearsal just get a good tone out of your amps and leave it alone. If you cant get your vocals on top what difference does it make? In most bands vocals should determine your levels. If you overblow your singer what happens, he either overblows his vocal chords or has trouble staying in pitch. When you get out and play live you need to have control over this or your band will suck soundwise.
Being loud doesnt make for good tone. It just shows immaturity. I know Ive been there and done that myself and still occasionally do this, but in the end I want the whole group to sound good.
In rehearsal try to set your amp levels comfortably over your drummer. Once you determine this level try to bring up your vocals to where you can hear everything cleanly.
Our band practices at our bassist studio. We mic the drums and me and the bassist run preamps straight in the board and we listen thru headphones. You can hear every nuance of your fellow players. This has made us a much tighter band than when we used to use amps and just blast each other.
Live Ive learned to get really good tones on my amp at reasonable volumes. A lot of places you play will tell you you are too loud anyway. Another thing that can happen is if you practice at extreme levels when you move out of the rehearsal room to a venue the sound pressure dropps dramatically and it doesnt sound or feel the same. SOme players have trouble with this.
I dont think a compressor or limiter is going to make a lot of difference, in fact it may just make more noise. If your pa is underpowered for what you are doing then pad down the drums some and reduce everyones volumes til you can hear the vocals well enough to rehearse.
Good luck this is all part of becoming a better musician. The sooner you learn to control the volume the quicker you will become a tighter better sounding band.
"A winks as good as nod to a blind man"