I need advice on how to make polygammy work ?

I am in a polygamous relationship. Im the first girlfriend. Hes brought his baby mama in now and i'm having difficulty adjusting to her being here but over all im doing very well. Im not jealous as i was when he first brought her in. But she is having a lot of difficulty going from monogamous to polygamous. She shouts and argues and doesnt understand how shes being disrespectful. She refuses to accept that we both need our alone time with him as well as our time all together. Can anyone give some advice how to get all of us to cope? It seems like im the only one coping with the change.