Need two profiles. Add one Child profile using Weighted routing. One additional trial endpoint, to the existing three, for the Child Profile is needed.
Note 1: Each Traffic Manager profile specifies a single traffic-routing method. However, there are scenarios that require more sophisticated traffic routing than the routing provided by a single Traffic Manager profile. You can nest Traffic Manager profiles to combine the benefits of more than one traffic-routing method.
Note 2: Weighted routing: Select Weighted routing when you want to distribute traffic across a set of endpoints based on their weight. Set the weight the same to distribute evenly across all endpoints.
Reference:
https://docs.microsoft.com/en-us/azure/traffic-manager/traffic-manager-nested-profiles
https://docs.microsoft.com/en-us/azure/traffic-manager/traffic-manager-routing-methods