Why won't his 1st wife join me fight the 3rd?

I met Francis six years ago; we now share two beautiful children. However, before settling down with him, he confessed that he was lawfully married but he wanted me to be his second wife.

First I did not buy his idea because I did not want to be in those shoes . But later I accepted because he showed me so much love.

When his first wife learnt about our relationship, she declared war towards me .I almost gave up but I was already pregnant with our first child.

However, recently I learnt that our husband got a third wife who is six months pregnant. It hurt me so much that I almost ran mad and sought help from a counsellor.

I became very desperate and contacted the first wife so that we join forces and get rid of the other woman. However, she was not bothered at all yet with me she moved heaven and earth to see that I leave our husband.

I believe we can triumph over this woman when we join forces but she has refused.

How do I persuade her, please help.

Confused