i would say talk to the presidents and see if they have any insight. it doesn't have to be an outright complaint - frame it as what you have and what you need.

explanation of issue & attempts to resolve, request support, suggestion for support: "i am unable to stay on top of this project with the current workload. i have attempted to contact my partners multiple times, but they are neither contributing to the proposal nor are they able to set aside time to work on it. what options do we have for additional support? would anyone else be able to fill in at this time?"