coparenting schedules

i need some help, my boyfriend of 4 years and i just split up. he has raised my oldest 2 daughters since i was pregnant with my second and my oldest was 18 months. 2 years ago, their dad took me to court and is back in the picture but both have been playing a role to my oldest 2 daughters. that being said, now that we’ve broken up idk what i’m supposed to do for my daughters. i dont want to rip their step dad from their lives but he and their bio dad dont get along for me to make it work with them both seeing them and sharing with me. i dont know what kind of schedule to do or how to explain this to a 6 and 4 year old. please anyone with similar experience or even some knowledge on coparenting plans with two fathers, please help