Complex sentence: We don't know much about Kerry-anne other than the fact her mother was Steve's ex, but he ran from being a father because he wasn't ready for a child, therefore his brother stepped up (now married to the mother).
Split into simpler sentences: We don't know much about Kerry-Anne other than the fact her mother was Steve's ex, but he ran from being a father because he wasn't ready for a child. Therefore, his brother stepped up (now married to the mother).