I think this would work. It's what Xfinity (Comcast) uses to split the single coax input for their service. One goes to my set top box and the other goes to their Xfinity Gateway.
https://www.ebay.com/itm/171371659404
Edit: You would need 2 more coax cables + 3 RCA Female to F Type Male RF Connector Coaxial Adapters