Thank you for the assistance Evan - this solved my problem. 

The list type of Organizations existed prior to the changes I am making and is in use within the application in other places. As such I was ideally hoping implement the cascade deletion without changing that type. However, a Parent/Child relationship as both you and @Iryna Mykhailova suggested is a great option for the automatic cascade deletion and I will definitely consider the benefits of that change. Thank you!

Thank you for the clarification. For the given situation, there would never exist multiple lists that hold the same organization object. Following your example, my tables would be as such. 

So that there would not exist a situation where a deletion of a list in GetOrgUpdatesResponse would result in any other list containing incorrect data.