Unfortunately, the option to train for multiple goals simultaneously is not currently available in JOIN and there are no plans to add this feature at this time.
In the meantime, the best approach is to set your first and most important goal in JOIN and train towards it. Once that event is completed, simply set your next goal and JOIN will build a plan to get you in the best possible shape for that one.
If you are racing every weekend, set your main target race as your primary goal and add your other races as planned rides in the week before each event. JOIN will then account for the extra load and adapt your training around them without disrupting your overall plan structure.
For more information on how to add a planned ride or race in JOIN, see this link