Well Jaime, I think that many of our Members will think that you are "living the dream" and I feel that you don't need much advice from me. It works for you all, your Girl friend is getting plenty of fucking so I presume that she is one happy and contented lady. Four lads,all sizes and skills to take care of her needs. You get to either watch or take part, nothing is done behind your back, it is all in the open, no cheating going on.
Most important is that none of you seem to be jealous of each other.
Maybe the only advice I can give is to say, don't spoil it. Never let jealousy take over, she likes and maybe even needs the increased attention. She has got used to having the freedom of choice and somehow I can not see her wishing to go back to One man, one woman. Plus would you like to return to ( what can be ) the bordom and worry of duty sex.
She as started to enjoy the fun of it and I can not see her wanting to give it up.
The lifestyle you have all selected comes in many forms. Sounds like she like to wants to sexualy humiliate you and it sounds like you like this. This may be the price you pay but guard against it going to far. I believe that the man of the house should still be master of his own Kingdom and since you allow these events you should be respected for it.