Copy Child Records to another object

Hi All,
Thank you for your help/recommendations in advance.

I have two objects, Event, and Event Role. For each Event, there are multiple roles needed. For example, We have a weekly Bingo night and for each night, there can be anywhere from 20-30 roles. Rather than having the user (admin) recreate the roles for each Event they create, I created two new objects, Event Template and, Event Role Template, which are made up of the same fields from Event and Event Role.

Now, when I am creating a new Event, I have a dropdown that shows all available templates. They choose the “Bingo” template and then I populate the Event information from the Template using Record Update on the form. However, that only allows me to create the Event. How can I select the records on the Event Role Template and copy them to the Event Role for the template selected? I am assuming an API will be needed but didn’t know if there were other options. Thanks so much. Charlie