I want to create a form in which customers can indicate information about a family calendar.

The form needs to list 12 months and for each month, a date, name and photo ID#

In the case of more than one milestones in a month, the user needs to be able to add another milestone in that month.

I do not believe any of our calendar widgets would allow for inputting additional data into the actual calendar.  All the widgets I checked either allow for selecting dates or comparing dates.

You could use a configurable list widget to set up multiple sets of different types of fields:

http://widgets.jotform.com/widget/configurable_list

This would allow users to add as many set of fields as they need.  Include a date field to allow for each set to have a specific date.