LiquidPlanner does not explicitly support multiple owners for one task.  This is a deliberate design decision which allows us to most accurately capture the effect of each individual contributor’s schedule. 

Modeling One Task With Multiple Owners

You can start by simply breaking one task into multiple tasks.  Assign each one to a different person and estimate just that person’s individual contribution.  This alone will give you an accurate schedule. 

You might prefer to take this a step further by creating a tasklist to contain the set of individual tasks.  The task list then represents a rollup of the individual tasks, and you would keep an eye on the rollup to see when the entire set of work (the “task”) will be completed:     

Notice that Liz, Mary Ellen and John will actually be starting their contribution at different times, based on other higher-priority work on each of their plates.