How do I defend myself against assault charges brought against me for defending a minor (my 9 year old son) and someone else (my fiancé) from a middle aged woman?

My son (9 year old) was allegedly assaulted by my next door neighbor at a communal park where a group kids were playing, my neighbors' grandson is said to have come to her crying that "someone" hurt him at the park. She took it upon herself to engage the incident directly with the kids with an average age of 10. She is said to have struck my son and verbally abused another 12 year old both of which were the only kids who came back screaming in pain from the altercation with her. No older witnesses were at the park when this happened. It was just her and the kids. The 2 crying kids came to report the incident to their mothers. I recieved a call from my fiancé to come home. When I got home I found the accuser with her hands around my fiancé in a threatening manner on the back of the fact that she has (the accuser) previously assaulted my fiancé and a case was opened with SAPS and nothing happened in that regard. As I came across seeing her I proceeded to remove her (accuser) from my fiancé she then tripped and fell to the floor, I approached her on the floor to pick her up and ask "what she did". I was overcome with so much emotion that I can't remember what happened thereafter. I remember after all that we called the cops who took independent statements as she was pressing charges against me and my fiancé pressed charges against her.